Add jobcacher to the managed set

[jonesbusy]

Fix #4287

Testing done

PLUGINS=jobcacher TEST=InjectedTest bash local-test.sh

Docker test should be skipped by https://github.com/jenkinsci/jobcacher-plugin/pull/375/files

Possible now 2.479 is on the bottom line

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue

[jonesbusy]

super green! Thanks @krisstern

[krisstern]

You are welcome @jonesbusy!

[basil]

FYI this should have been in test scope unless it is needed to compile the sample plugin. I'll fix this in one of my next few PRs, so this comment is just for future reference.