Require release related label on PRs against main branch.

.github/workflows/require_label.yml

@@ -0,0 +1,18 @@
+name: Require PR Labels
+
+on:
+  pull_request:
+    types: [opened, labeled, unlabeled, synchronize]
+    branches: [main]
+
+jobs:
+  require_label:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: mheap/github-action-required-labels@v2
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          mode: exactly
+          count: 1
+          labels: "Release: Major, Release: Minor, Release: Patch, No release"