Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/update.yml

@@ -9,7 +9,7 @@ jobs:
   update:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Use Node.js
         uses: actions/setup-node@v4
       - run: npm install