Bump macOS to macos-14 on GitHub Actions

[0xEAB]

Rationale: actions/runner-images#13046

This might need a maintainer to tune the configured requirement settings — similar to dlang/dmd#21985 (comment).

I’ve also removed the version number from job_name — this matches how the Windows job is named and would make the upgrade to a macos-15 based image less painful.

[dlang-bot]

Thanks for your pull request, @0xEAB!

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#10928"

[0xEAB]

@rikkimax By the way, macos-14 seems to be the Arm64 image.
But given that DMD uses the same one, I suppose that’s fine.

See also:
https://github.com/actions/runner-images/blob/93af8363f95b5996210fa31500089dd74acd0817/README.md

[rikkimax]

Branch protection fixed, merging.