github: add workflow sync-fork

From https://gist.github.com/DewaldDeJager/518f6814049a0f7763642ec02f62cabf.

Signed-off-by: Camilla Conte <[email protected]>

.github/workflows/sync-fork.yaml

@@ -0,0 +1,16 @@
+name: sync-fork
+on:
+  schedule:
+    - cron: '0 0 * * *'
+  workflow_dispatch: { }
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - run: gh repo sync $REPOSITORY -b $BRANCH_NAME
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          REPOSITORY: ${{ github.repository }}
+          BRANCH_NAME: ${{ github.ref_name }}