Update actions/checkout action to v6

Author: renovate-bot

.github/workflows/check.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: '0'
           show-progress: 'false'