PR Summary

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).

On anything after #19255, when resizing some plots (on PyQt5 5.15.4) I get:

>>> Traceback (most recent call last):
  File "/home/larsoner/python/matplotlib/lib/matplotlib/backends/backend_qt.py", line 336, in resizeEvent
    if frame.f_code is frame.f_back.f_code:  # Prevent PyQt6 recursion.
AttributeError: 'NoneType' object has no attribute 'f_code'

This PR fixes this problem using getatttr. I'm not sure how to make a good unit-test for this...