The font cache (written to ~/.cache/matplotlib) may already contain entries indexed before this env var was set. Does this change correctly invalidate pre-existing cache entries, or could stale cache hits still surface system fonts?

This ensures that only internal fonts are found: https://github.com/matplotlib/matplotlib/pull/31486/changes#diff-aca801331b4c856bff720af0575b9ad63f402c893abd7d939e5547ba961ee324R1525-R1526

Not sure if it needs a What's New? entry; probably too niche for that.

I think a short one couldn't hurt?

re-ran the failing 3.11 min version test.

3.11 minver passed this time; I'll ignore AppVeyor as the build shows all tests passed (and it just got hung up on the post-testing phases.)