repo = 'https://github.com/jmacloue/mypwgen-pl.git'
branch = 'ad0f6e4'

pipeline {
    agent any
    stages {
        stage("GitSCM") {
            steps {
                checkout([$class: 'GitSCM',
                          userRemoteConfigs: [[url: repo]],
                          branches: [[name: branch]],
                         ])
            }
        }
        
        stage("shorthand") {
            steps {
                git url: repo, branch: branch
            }
        }
    }
}

...
 > git fetch --tags --force --progress -- https://github.com/jmacloue/mypwgen-pl.git +refs/heads/*:refs/remotes/origin/* # timeout=10
 > git rev-parse ad0f6e4^{commit} # timeout=10
Checking out Revision ad0f6e453986b1a068d1d6cab4aef37f254ab86e (detached)
...
 > git rev-parse refs/remotes/origin/ad0f6e4^{commit} # timeout=10
 > git rev-parse refs/remotes/origin/origin/ad0f6e4^{commit} # timeout=10
 > git rev-parse origin/ad0f6e4^{commit} # timeout=10
...
ERROR: Couldn't find any revision to build. Verify the repository and branch configuration for this job.
Finished: FAILURE

...
 > git rev-parse origin/master^{commit} # timeout=10
Checking out Revision ad0f6e453986b1a068d1d6cab4aef37f254ab86e (origin/master)
...
 > git rev-parse refs/remotes/origin/master^{commit} # timeout=10
 > git rev-parse refs/remotes/origin/origin/master^{commit} # timeout=10
Checking out Revision ad0f6e453986b1a068d1d6cab4aef37f254ab86e (refs/remotes/origin/master)
...