Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/pages.yml

@@ -31,7 +31,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1.302.0
         with: