CI not passing because `macos-12` runner for GH Actions no longer exists

[DavidMazarro]

According to the GitHub hosted runner docs, the macos-12 runner is no longer offered. We should change the macOS runner we are using for tests in the CI to one of the available ones, ideally macos-latest for future-proofing.

[sestrella]

#85 tackled this issue

[DavidMazarro]

@sestrella Thank you! Keep in mind that we will still need to eventually phase out the macos-13 runner (and with it, Intel macOS support). For now, I think we are good.