chore: use bats junit formatter only in CI

[lemeurherve]

This PR removes the junit formatter and result storage when executing make test locally (as $CI is set to true by Jenkins when running on CI), for a better contributor experience:

• Colored output
• No XML markup
• Test results displayed one after one instead of hanging until all tests passed
• Possibility to cancel the running tests while still seing the first results (currently return printf: write error: Broken pipe on cancel)

Before:

After:

Testing done

make test + CI

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