chore(ci): improve error handling and push only ref

.gitea/workflows/sync.yaml

@@ -15,6 +15,8 @@ jobs:
     - ubuntu-latest
     steps:
     - uses: actions/checkout@v4.2.2
+      with:
+        fetch-depth: 0
     - name: Configure SSH client
       run: |
         mkdir ~/.ssh || true
@@ -30,7 +32,7 @@ jobs:
         EOF
     - name: Push
       run: |
-        git push ssh://aur@aur.archlinux.org/mint-backgrounds.git ${{ github.ref }}
+        git push ssh://aur@aur.archlinux.org/mint-backgrounds.git 'HEAD:refs/heads/master'
     - name: Remove SSH client configuration
       run: |
         rm -rf ~/.ssh