Fix merge queue (open-telemetry#2143)

Author: trask

.github/workflows/build-pull-request.yml

@@ -8,7 +8,7 @@ permissions:
   contents: read
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
 
 jobs: