Enable banning of junit4 dependencies.

[Tzrlk]

This will improve security and plugin health score as reported by https://plugins.jenkins.io/pagerduty/healthscore/ and outlined in jenkinsci/plugin-pom#1178

Testing done

No testing beyond standard build required.

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 demonstrate the feature works or the issue is fixed