Fix labeler configuration (#6344)

# Description

In PR #6328 I have added an automatic maintenance label when something
is edited pre-commit. But I wrongly understand actions/lableler
documentation and thought that the bug was fixed, that is true, but it
is fixed in v5 branch, not backported to v4.

v5 has been from a long time (since May) in the release process.

actions/labeler#112

.github/workflows/labeler.yml

@@ -13,3 +13,5 @@ jobs:
     - uses: actions/labeler@v4
       with:
         repo-token: "${{ secrets.GITHUB_TOKEN }}"
+        # sync-labels need to be removed when upgrade to v5 of labeler
+        sync-labels: ''