PR Summary

Otherwise, a new version will be installed in the isolated build environment, and Matplotlib will fail to import in an existing environment with older NumPy.

According to its docs, this should be okay even though we target a newer version at runtime, and this linkage may possibly go away if we move to pybind11 anyway.

PR Checklist

Tests and Styling

• [n/a] Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• [n/a] Documentation is sphinx and numpydoc compliant (the docs should build without error).
• [n/a] New plotting related features are documented with examples.

Release Notes

• [n/a] New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• [n/a] API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• [n/a] Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst