PR Summary

I got some TemporaryDirectory ResourceWarning's in a sphinx-gallery-based doc builds with matplotlib animations, so I started trying to replicate them with some minimal code. I couldn't, but it looked like there weren't any explicit _repr_html_ tests in the test_animation.py code, so I figured I'd open a PR to add some basic ones (these were my minimal examples that showed no problems at the mpl end).

PR Checklist

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (run flake8 on changed files to check).
• New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• Conforms to Matplotlib style conventions (install flake8-docstrings and pydocstyle<4 and run flake8 --docstring-convention=all).
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).