PR Summary

This PR is a second attempt to fix #18246. Perhaps if we are careful to reset tkinter between tests, things will be less flaky. There is a lot of logic in the cpython test suite dedicated to this.

As with #18261, draft PR to engage CI.

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/next_api_changes/* if API changed in a backward-incompatible way