The Matplotlib test suite can be run from outside of the root git
directory, e.g. with

pytest --pyargs matplotlib.tests.test_backend_nbagg

(mplcairo explicitly relies on that to reuse the Matplotlib test suite).

To ensure this, find the example notebook relative to the path of the
test module, rather than relative to the current working directory.

(Marking as release critical to avoid causing difficulties to mplcairo's test suite, but I can always xfail that test instead from mplcairo otherwise.)

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code is PEP 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/api_changes.rst if API changed in a backward-incompatible way