Add trigger for push to main branch for sync'ing with master (#2387)

* gh action for merging main to master on pr merge

* remove pull_request as trigger. only use push, that is after merging the pull_request

Author: amanjeev

.github/workflows/sync-master-from-main.yml

@@ -0,0 +1,21 @@
+name: sync master from main
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  sync-branches:
+    runs-on: ubuntu-latest
+    name: Keep master and main in sync until master is done
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Merge master <- main
+        uses: devmasx/merge-branch@master
+        with:
+          type: now
+          from_branch: main
+          target_branch: master
+          github_token: ${{ secrets.GITHUB_TOKEN }}