PR Summary

Closes #20635

@jklymak the places I was using cbar.patch, using cbar.ax was the correct solution (e.g., cbar.ax.set_facecolor instead of cbar.patch.set_facecolor). The message now reads:

The patch attribute was deprecated in Matplotlib 3.5 and will be removed two minor releases later. Use ax instead.

PR Checklist

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