[JENKINS-75879] GStringTemplateEngine causes memory leak in class loading

[jgarciacloudbees]

See JENKINS-75879.

Testing done

Manual testing performed related to the current case of use described on JENKINS-75879.

• The system works properly and the pipeline is executed with no issues.
• Comparing the heap dump from before and after the changes we can see:
  • In the previous version there were a lot of ParallelLocks for the classess jenkins.util.URLClassLoader2 related to objects similar to: groovy.tmp.templates.GStringTemplateScript*
  • In the new version, such ParallelLocks are not created.

Proposed changelog entries

• Fix memory leak in Java class loading for the GStringTemplateEngine class.

Proposed changelog category

/label bug

Proposed upgrade guidelines

N/A

Submitter checklist

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• There is automated testing or an explanation as to why this change has no tests.
• [] New public classes, fields, and methods are annotated with @Restricted or have @since TODO Javadocs, as appropriate.-> N/A, no new items created
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• For new APIs and extension points, there is a link to at least one consumer. -> N/A no new APIs or extension points

Desired reviewers

@jglick, @Dohbedoh

Before the changes are marked as ready-for-merge:

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[dukhlov]

Covered by https://github.com/jenkinsci/jenkins/pull/10659/files#diff-0dd3c7930da03922fff631a2cf06fbfda9b9bc688a4e5804fceda225147778a6L2412

[A1exKH]

LGTM.

[Dohbedoh]

LGTM.
I am wondering if we want to also ignore classes from other String template implementation such as StreamingTemplateScript* and XmlTemplateScript* ?

[timja]

/label ready-for-merge

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This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

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