Throttle Concurrent Builds UI broken after <table> to <div> layout migration

The xunit plugin contains tabular markup on some form elements and will probably present issues with the tables-to-divs changes in https://issues.jenkins-ci.org/browse/JENKINS-62437

At least the following files may be affected:

• https://github.com/jenkinsci/throttle-concurrent-builds-plugin/blob/master/src/main/resources/hudson/plugins/throttleconcurrents/ThrottleJobProperty/global.jelly
• https://github.com/jenkinsci/throttle-concurrent-builds-plugin/blob/master/src/test/java/hudson/plugins/throttleconcurrents/ThrottleJobPropertyTest.java

Some migration recipes can be found on https://www.jenkins.io/doc/developer/views/table-to-div-migration/