sshagent(credentialsId: ["my-ssh-credentials"]) {
  sh """
    git tag some_tag
    git push origin some_tag
  """
}

+ which ssh-agent
/usr/bin/ssh-agent
[Pipeline] dirRunning in c:\jenkins\workspace\test\test-ssh
[Pipeline] {
[Pipeline] sshagent
[ssh-agent] Using credentials software.development@company.com (my-ssh-creds)
[ssh-agent] Looking for ssh-agent implementation...
[ssh-agent]   Exec ssh-agent (binary ssh-agent on a remote machine)
$ ssh-agent
[ssh-agent] FATAL: Could not find a suitable ssh-agent provider
[ssh-agent] Diagnostic report
[ssh-agent] * Exec ssh-agent (binary ssh-agent on a remote machine)
[ssh-agent]     java.lang.StringIndexOutOfBoundsException: begin 13, end -1, length 0
[ssh-agent]     	at java.base/java.lang.String.checkBoundsBeginEnd(String.java:3319)
[ssh-agent]     	at java.base/java.lang.String.substring(String.java:1874)
[ssh-agent]     	at com.cloudbees.jenkins.plugins.sshagent.exec.ExecRemoteAgent.getAgentValue(ExecRemoteAgent.java:157)
[ssh-agent]     	at com.cloudbees.jenkins.plugins.sshagent.exec.ExecRemoteAgent.parseAgentEnv(ExecRemoteAgent.java:141)
[ssh-agent]     	at com.cloudbees.jenkins.plugins.sshagent.exec.ExecRemoteAgent.<init>(ExecRemoteAgent.java:69)
[ssh-agent]     	at com.cloudbees.jenkins.plugins.sshagent.exec.ExecRemoteAgentFactory.start(ExecRemoteAgentFactory.java:84)
[ssh-agent]     	at com.cloudbees.jenkins.plugins.sshagent.SSHAgentStepExecution.initRemoteAgent(SSHAgentStepExecution.java:158)
[ssh-agent]     	at com.cloudbees.jenkins.plugins.sshagent.SSHAgentStepExecution.start(SSHAgentStepExecution.java:64)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.DSL.invokeStep(DSL.java:322)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:196)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:124)
[ssh-agent]     	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[ssh-agent]     	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[ssh-agent]     	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[ssh-agent]     	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
[ssh-agent]     	at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
[ssh-agent]     	at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
[ssh-agent]     	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1225)
[ssh-agent]     	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
[ssh-agent]     	at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:41)
[ssh-agent]     	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
[ssh-agent]     	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
[ssh-agent]     	at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:180)
[ssh-agent]     	at org.kohsuke.groovy.sandbox.GroovyInterceptor.onMethodCall(GroovyInterceptor.java:23)
[ssh-agent]     	at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:163)
[ssh-agent]     	at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:178)
[ssh-agent]     	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:182)
[ssh-agent]     	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
[ssh-agent]     	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
[ssh-agent]     	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
[ssh-agent]     	at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:17)
[ssh-agent]     	at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:90)
[ssh-agent]     	at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:116)
[ssh-agent]     	at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:85)
[ssh-agent]     	at jdk.internal.reflect.GeneratedMethodAccessor298.invoke(Unknown Source)
[ssh-agent]     	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[ssh-agent]     	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
[ssh-agent]     	at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
[ssh-agent]     	at com.cloudbees.groovy.cps.impl.ClosureBlock.eval(ClosureBlock.java:46)
[ssh-agent]     	at com.cloudbees.groovy.cps.Next.step(Next.java:83)
[ssh-agent]     	at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:152)
[ssh-agent]     	at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:146)
[ssh-agent]     	at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:136)
[ssh-agent]     	at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:275)
[ssh-agent]     	at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:146)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:51)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:187)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:420)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:330)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:294)
[ssh-agent]     	at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:67)
[ssh-agent]     	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[ssh-agent]     	at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:139)
[ssh-agent]     	at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:30)
[ssh-agent]     	at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:70)
[ssh-agent]     	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
[ssh-agent]     	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[ssh-agent]     	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
[ssh-agent]     	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
[ssh-agent]     	at java.base/java.lang.Thread.run(Thread.java:829)
[Pipeline] // sshagent
[Pipeline] }
[Pipeline] // dir
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Also:   org.jenkinsci.plugins.workflow.actions.ErrorAction$ErrorId: f49e91cd-8d6f-4c68-ab57-7bdb01477e32
java.lang.RuntimeException: [ssh-agent] Could not find a suitable ssh-agent provider.
	at com.cloudbees.jenkins.plugins.sshagent.SSHAgentStepExecution.initRemoteAgent(SSHAgentStepExecution.java:176)
	at com.cloudbees.jenkins.plugins.sshagent.SSHAgentStepExecution.start(SSHAgentStepExecution.java:64)
	at org.jenkinsci.plugins.workflow.cps.DSL.invokeStep(DSL.java:322)
	at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:196)
	at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:124)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
	at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1225)
	at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
	at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:41)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
	at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:180)
	at org.kohsuke.groovy.sandbox.GroovyInterceptor.onMethodCall(GroovyInterceptor.java:23)
	at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:163)
	at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:178)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:182)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:152)
	at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:17)
	at WorkflowScript.run(WorkflowScript:21)
	at ___cps.transform___(Native Method)
	at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:90)
	at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:116)
	at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:85)
	at jdk.internal.reflect.GeneratedMethodAccessor298.invoke(Unknown Source)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
	at com.cloudbees.groovy.cps.impl.ClosureBlock.eval(ClosureBlock.java:46)
	at com.cloudbees.groovy.cps.Next.step(Next.java:83)
	at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:152)
	at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:146)
	at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:136)
	at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:275)
	at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:146)
	at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
	at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:51)
	at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:187)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:420)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:330)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:294)
	at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:67)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:139)
	at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:30)
	at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:70)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:829)
Finished: FAILURE