Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/jekyll.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Setup node
         uses: actions/setup-node@v4
         with: