CI: Pin to macOS 12 runner images instead of macos-latest (GiHub Actions)

[DeeDeeG]

Identify the Bug

Alternative to #996

(PR body below is copied from #996 and lightly modified to reflect macos-12 runner image rather than macos-13.)

Was discussed in Discord: https://discord.com/channels/992103415163396136/1236740088487219320

To recap: There is an issue with the libiconv library apparently not being available in macOS 14 out of the box.

Description of the Change

Pin GitHub Actions macOS runner images to macOS 12 (macos-12), instead of macos-latest which is now resolving to macos-14 (which is ARM64-based) as of some point in April for us.

Going for this solution as the macos-latest runner images now refer to macOS 14 on ARM64 ("Apple Silicon"), which is a big change and not one we're (I'm?) prepared to migrate to just at this moment, besides that it doesn't build on macOS 14 out of the box due to an issue of libiconv apparently not being compatible or available (?) out of the box. This should get us passing CI faster while we evaluate what we want to do about macOS 14/ARM64.

See:

• https://github.blog/changelog/2024-01-30-github-actions-introducing-the-new-m1-macos-runner-available-to-open-source/
  • "GitHub Actions: Introducing the new M1 macOS runner available to open source!"
• https://github.blog/changelog/2024-01-30-github-actions-macos-14-sonoma-is-now-available/
  • "GitHub Actions: macOS 14 (Sonoma) is now available"
• https://github.com/actions/runner-images/tree/7bb1d84f7071bfa9c350d7552d9631d9a69bfdb0?tab=readme-ov-file#available-images

Alternate Designs

First of all, see #966, this is mainly being done in response to that PR having the same libiconv issue as macOS 14 runners do.

Could also try and build on macOS 14, which may be possible. Notes from @savetheclocktower on how to get superstring to build on macOS 14, from the Discord thread:

yeah, so this was definitely about libiconv. I had it installed via homebrew already, so i just needed to do export CPPFLAGS="-I/usr/local/opt/libiconv/include" and then run npm run build again — that fixed the error on my machine

Not doing that for now, since if it builds on macOS 12 (macos-12 runner image) without changes, that's a faster fix and a neater/tidier small scope.

Possible Drawbacks

This PR means not building on macOS 14 or ARM right away, even though the resolution of macos-latest has been updated to macos-14 and it is thus the "default" / perhaps best-supported macOS runner for GitHub Actions now (?). But we weren't really expecting to build on macOS 14 all of a sudden, either. (Up until very recently (some time in April) macos-latest runner images resolved to macos-12 on x86-64.)

So, arguably no drawbacks.

Verification Process

This is a CI fix, so I will be verifying it by checking whether CI passes or not.

Release Notes

N/A

[confused-Techie]

CI Passes here, and as that's it's purpose looks good to me. Would also love to get this updated on all of our currently failing PRs that exist in the wild as of now with this issue.

Thanks a ton for getting this one together!