Fix condition

Author: tstellar

.github/workflows/premerge.yaml

@@ -136,8 +136,10 @@ jobs:
     concurrency:
       group: ${{ github.workflow }}-macos-${{ github.event.pull_request.number || github.sha }}
       cancel-in-progress: true
-    if: >- 
-      github.repository_owner == 'llvm'
+    if: >-
+      github.repository_owner == 'llvm' &&
+      (startswith(github.ref_name, 'release/') ||
+       startswith(github.base_ref, 'release/'))
     steps:
       - name: Checkout LLVM
         uses: actions/checkout@v4