Summary

I just created a new mpl-dev environment from the conda yml file. I think this was the first time I had python 3.13 for this. The black version installed was 19.3b0, which is pretty old and caused a failure in boilerplate.py (due to psf/black#2964).

I think the problem is that we currently have black pinned to <24 to keep the formatting stable. However black versions 20-23 are only available for python<3.13.

Proposed fix

Bump the black version pin.