chore: skip OS X aarch64 CI only in merge groups

This commit changes the CI release builds to skip the macOS aarch64 build
only in case they are executed as part of a merge group. Today, these
CI builds are also skipped when tagging a branch in a lean4 fork, which
means builds from such tags cannot be tested on an macOS laptop.

This resolves #8333.

Author: tobiasgrosser

.github/workflows/ci.yml

@@ -138,6 +138,7 @@ jobs:
             // use large runners where available (original repo)
             let large = ${{ github.repository == 'leanprover/lean4' }};
             const isPr = "${{ github.event_name }}" == "pull_request";
+            const isMerge = "${{ github.event_name }}" == "merge_group";
             let matrix = [
               /* TODO: to be updated to new LLVM
               {
@@ -229,7 +230,7 @@ jobs:
                 // 2. To skip it in merge queues as it takes longer than the Linux build and adds
                 //    little value in the merge queue
                 // 3. To run it in release (obviously)
-                "check-level": isPr ? 0 : 2,
+                "check-level": isMerge ? 2 : 0,
                 "secondary": isPr,
               },
               {