Thanks @dstansby, and my apologies for introducing the bug! Your fix looks good to me so far based on: https://github.com/matplotlib/matplotlib/actions/runs/13819709516/job/38661817676?pr=29748#step:10:285

I am also wondering, though: given that tests passed without the relevant packages installed at all -- could we remove their installation step from the MacOS CI script? It seems it was originally introduced as a workaround to a MacOS 10.12 bug -- so maybe it is no longer required.

(that wasn't what I planned to show with my change; but inadvertently, it seems that's what I did)

Ah, no, my mistake; you mentioned that the absence of the packages causes the failing test to be skipped. In that case: let's apply this fix, and continue the investigation into why the version upgrade is blocked.

Ah, no, my mistake; you mentioned that the absence of the packages causes the failing test to be skipped. In that case: let's apply this fix, and continue the investigation into why the version upgrade is blocked.

And indeed I can confirm that with my flawed attempt at a fix (38cf554), the test_interactive_backend[toolbar2-MPLBACKEND=gtk4cairo-BACKEND_DEPS=cairo,gi] test, the failed test we're aiming to fix, is skipped on MacOS 14: https://github.com/matplotlib/matplotlib/actions/runs/13800489129/job/38630884101#step:14:311

(sorry for being verbose; I'd like to be transparent and also keep some notes in case I need to pick up again from forgotten context in future)

I'm going merge this on my review + @jayaddison review + fixing CI.