Add github action to ensure PRs are labeled. (shader-slang#4130)

* Add github action to ensure PRs are labeled.

* Update.

* Fix.

* Fix

* Fix

* more Fix

* more fix.

* try.

* fix

* another try.

---------

Co-authored-by: ArielG-NV <159081215+ArielG-NV@users.noreply.github.com>

Author: csyonghe

.github/workflows/ensure-pr-label.yml

@@ -0,0 +1,18 @@
+name: Verify PR Labels
+on:
+  pull_request:
+    types: [opened, labeled, unlabeled, synchronize]
+jobs:
+  label:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+    steps:
+      - uses: mheap/github-action-required-labels@v5
+        with:
+          mode: exactly
+          count: 1
+          labels: |
+            pr: non-breaking
+            pr: breaking change