chore(deps): update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/sync-labels.yml

@@ -7,7 +7,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: micnncim/action-label-syncer@v1
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}