Trigger auto-request-review only for master branch

.github/workflows/auto_request_review.yml

@@ -10,7 +10,7 @@ jobs:
   auto-request-review:
     name: Auto Request Review
     runs-on: ubuntu-latest
-    if: ${{ github.repository == 'ruby/ruby' }}
+    if: ${{ github.repository == 'ruby/ruby' && github.base_ref == 'master' }}
     steps:
       - name: Request review based on files changes and/or groups the author belongs to
         uses: necojackarc/auto-request-review@6a51cebffe2c084705d9a7b394abd802e0119633 # v0.12.0