add Git CI for sync with upstream repo

Git/.woodpecker/.sync.yaml

@@ -0,0 +1,29 @@
+when:
+  event: [ cron, manual ]
+  cron: "sync"
+
+clone:
+  - name: clone
+    image: woodpeckerci/plugin-git
+    settings:
+      depth: 0
+      lfs: false
+      partial: false
+
+steps:
+  - name: sync
+    image: docker.io/alpine/git
+    environment:
+      MAIL:
+        from_secret: mail
+      CODEBERG_TOKEN:
+        from_secret: codeberg_token
+    commands:
+      - git remote set-url origin https://$CODEBERG_TOKEN@codeberg.org/<YOUR_FORK>
+      - git config user.email $MAIL
+      - git config user.name "Woodpecker CI"
+      - git remote add upstream https://codeberg.org/<UPSTREAM_REPO>
+      - git fetch upstream
+      - git checkout main
+      - git merge upstream/main
+      - git push origin main