[ci] do not block pull requests on cache_bitstreams

Signed-off-by: Gary Guo <[email protected]>

.github/workflows/ci.yml

@@ -686,3 +686,22 @@ jobs:
       - name: Check for unrunnable tests
         run: ./ci/scripts/check-unrunnable-tests.sh
         continue-on-error: true
+
+  # The branch protection will gate on "Merge blocker" and we use these jobs with conditional names to
+  # gate on different jobs for merge queue and pull request checks.
+  merge_blocker_pr:
+    name: Merge blocker${{ github.event_name == 'pull_request' && '' || ' (Skipped)' }}
+    runs-on: ubuntu-latest
+    needs: quick_lint
+    if: ${{ github.event_name == 'pull_request' }}
+    steps:
+      - name: Complete
+        run: 'true'
+  merge_blocker_merge:
+    name: Merge blocker${{ github.event_name == 'merge_group' && '' || ' (Skipped)' }}
+    runs-on: ubuntu-latest
+    needs: cache_bitstreams
+    if: ${{ github.event_name == 'merge_group' }}
+    steps:
+      - name: Complete
+        run: 'true'