Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/check_links.yaml

@@ -13,7 +13,7 @@ jobs:
     permissions:
       issues: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           path: main
           filter: "blob:none"