rebuild when labels change, so that we can trigger the right actions (#11725)

Author: zeitlinger

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

@@ -2,6 +2,11 @@ name: Build pull request
 
 on:
   pull_request:
+    types:
+      - labeled
+      - opened
+      - synchronize
+      - reopened
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number }}