Backport tests from PR #4692 to 3.x

[stevenaw]

Backport tests from #4692
To verify the functionality from 3.x that we're restoring. Relates to #4598

This PR also switches the macos image on github actions to target specifically macos-12 in order to work around this NET5-related issue: dotnet/runtime#48068. It seems this may be the first time we're running CI on the 3.x branch since macos-latest was changed to macos-14 and the newer silicon architecture.

[stevenaw]

@nunit/framework-team
I've noticed net5 tests still running on the 3.x branch are now failing on macos. That runtime has been EOL for a while and is no longer used in main. Any objections to me removing it from 3.x either within this PR or separately?

[OsirisTerje]

I believe we have stated that 3.X will continue to support these OOD frameworks.
Can't we just disable that test from MacOS, and make a note of it ?
I believe we do have some more of those, which have been marked the same way, I think using the Platform attribute.

[stevenaw]

Thanks @OsirisTerje I can try to take a closer look.

[stevenaw]

Huh interesting. Thanks for having me take a closer look here @OsirisTerje
I had thought it was a NET5 EOL issue but the real thing here was that macos-latest switched to macos-14 which uses newer Apple Silicon / M1+. It appears this was a known issue a few years back with NET5 not working there in all cases: dotnet/runtime#48068

Switching the image from macos-latest down to macos-12 seems to have solved it. macos-12 is still supported and not yet deprecated based on https://github.com/actions/runner-images?tab=readme-ov-file.

I think this is ready to switch out of Draft

[OsirisTerje]

@stevenaw Awesome! And agree!

[OsirisTerje]

LGTM