Add "Do Not Merge" GH Action to block PRs with "DO-NOT-MERGE" label (#…

…18724)

* gh action: do-not-merge

* gh action: do-not-merge update

* gh action: Do Not Merge - use github.event.pull_request

Co-authored-by: Mark Stacey <markjstacey@gmail.com>

---------

Co-authored-by: Mark Stacey <markjstacey@gmail.com>

.github/workflows/do-not-merge.yml

@@ -0,0 +1,17 @@
+# Fails the pull request if it has the "DO-NOT-MERGE" label
+
+name: Check "DO-NOT-MERGE" label
+
+on:
+  pull_request:
+    types: [opened, reopened, labeled, unlabeled, synchronize]
+
+jobs:
+  do-not-merge:
+    runs-on: ubuntu-latest
+    if: ${{ contains(github.event.pull_request.labels.*.name, 'DO-NOT-MERGE') }}
+    steps:
+      - name: 'Check for label "DO-NOT-MERGE"'
+        run: |
+          echo 'This check fails PRs with the "DO-NOT-MERGE" label to block merging'
+          exit 1