Perform merge-conflict label checks, via GitHub Actions

Author: pradyunsg

.github/workflows/label-merge-conflicts.yml

@@ -0,0 +1,12 @@
+on:
+  push:
+    branches: [main]
+
+jobs:
+  label-merge-conflicts:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: pradyunsg/auto-label-merge-conflicts@v3
+        with:
+          CONFLICT_LABEL_NAME: "needs rebase or merge"
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}