Update actions/checkout action to v6 (#13)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/sync.yml

@@ -15,7 +15,7 @@ jobs:
       issues: write # Required for creating labels
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Setup Node.js
         uses: actions/setup-node@v4