Show test results for tests with warnings

[koesie10]

This fixes tests with warnings that would error out instead of showing the diff. It now results in:

The warning being shown in the actual output is expected and is part of normal testing of CodeQL. I don't think that's something that can be changed.

Closes #3386

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[charisk]

LGTM.

Optional: can we add any tests around this, or is the area not generally covered by tests?

[koesie10]

Optional: can we add any tests around this, or is the area not generally covered by tests?

There aren't many tests for this area, but I've added a test for this specific behavior to the existing test.