Use of `macos-12` runner is coming to an end.

[WilliamJamieson]

According to actions/runner-images#10721, the macos-12 image was deprecated on 10-7-24, and has stopped being supported as of yesterday (12/3/24). Due to this we have begun to see failures in our CI.

I suspect that

github-actions-workflows/tools/load_build_targets.py

Line 10 in e772a71

"macos": "macos-12",

and

github-actions-workflows/tools/tox_matrix.py

Line 142 in e772a71

item["os"] = "macos-12"

will need to be updated to macos-13.

Note that this may mean that x86 support will become more difficult in the future.