Replace references to JDK17 by default to JDK21 (backport of #534 into stable-2.528)

[lemeurherve]

Ref:

• LTS 2.528.2 release checklist jenkins-infra/release#772

Testing done

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

[MarkEWaite]

Thanks!