ci: enable label synchronization in PR labeler workflow

This ensures that labels remain consistent by automatically syncing them.

Author: eazyhozy

.github/workflows/pr-labeler.yml

@@ -7,3 +7,5 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/labeler@v6
+        with:
+          sync-labels: true