Problem

Automated testing of third party packages against the latest matplotlib currently requires installing from source which takes quite a while.

Proposed solution

Add a github action (with cibuildwheel maybe?) that builds the latest matplotlib on one or a few OSes x python versions. Somethign like:

Python 3.8 and 3.9 on latest ubuntu

These wheels should then be uploaded to a consistent place (maybe somewhere on maptlotlib.org?) with a clear naming scheme so it's easy to install then from a scheduled github action.