chore(deps): update actions/checkout action to v6

| datasource  | package          | from | to |
| ----------- | ---------------- | ---- | -- |
| github-tags | actions/checkout | v5   | v6 |


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

Author: renovate[bot]

.github/workflows/sync.yaml

@@ -19,12 +19,12 @@ jobs:
       contents: write
     steps:
       - name: Checkout API repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           token: ${{ secrets.REPO_PAT }}
 
       - name: Checkout cloudnative-pg repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           path: cloudnative-pg
           repository: cloudnative-pg/cloudnative-pg