Test remove prototype from core

[timja]

jenkinsci/jenkins#7781

Testing done

Submitter checklist

Beta Give feedback

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

[basil]

The only new failure here (compared to 2.415) is plugins.MatrixPluginTest#run_configurations_on_with_a_given_label which does not surprise me given that jenkinsci/matrix-project-plugin#168 has not been merged/released.

[basil]

Green now =)