ci: both way repo sync

.github/workflows/sync.yml

@@ -0,0 +1,17 @@
+name: Sync with private repo
+
+on:
+  push:
+    branches: [ master ]
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Add remote
+        run: git remote add overhangio https://${{ secrets.GIT_USERNAME }}:${{ secrets.GIT_PASSWORD }}@git.overhang.io/core/tutor-xqueue.git
+      - name: Push
+        run: git push overhangio master