chore: skip OS X aarch64 CI only in merge groups

[tobiasgrosser]

This PR enables the build of all artifacts for custom releases, e.g., releases outside the main lean4 repository.

This resolves #8333.

[tobiasgrosser]

I believe this does the right thing, but the merge_group part has not been tested. @Kha, I would appreciate a careful refview.

[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 88078930a92aa55089e936a5fe8e99ec65ab2ceb --onto 29cc75531a5a0e8626fa5e96371e7ceb98877782. You can force Mathlib CI using the force-mathlib-ci label. (2025-05-14 10:49:57)

[Kha]

Wouldn't it make more sense to use the same level for custom releases as for standard releases, i.e. building all platforms?

[tobiasgrosser]

Potentially, but I am a bit unsure how this would translate into code. Alternatively, I guess I can check for github.event_name == 'push' && contains(github.ref, 'refs/tags/'), and the raise the check_level to 2. Is that what you have in mind?

[Kha]

Yes, I think you can replace the check for steps.set-release.outputs.RELEASE_TAG with that. But let's get @kim-em's input as well.

[tobiasgrosser]

Yes, I think you can replace the check for steps.set-release.outputs.RELEASE_TAG with that. But let's get @kim-em's input as well.

I introduced a separate step to check for custom releases. This works well, as can be seen here: https://github.com/opencompl/lean4/actions/runs/15029737370