[llvm] workflows/premerge: Add macOS testing for release branch (PR #124303)

[Aiden Grossman via llvm-commits]

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@@ -10,6 +10,7 @@ on:
   push:
     branches:
       - 'main'
+      - 'release/**'
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boomanaiden154 wrote:

Do you only want this for post-submit testing on the release branch? Is this just for testing currently similar to what we're doing for Linux?

https://github.com/llvm/llvm-project/pull/124303