chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -16,7 +16,7 @@ jobs:
       MDBOOK_VERSION: '0.4.40'
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup deno
         uses: denoland/setup-deno@v1

.github/workflows/deploy.yaml

@@ -28,7 +28,7 @@ jobs:
       MDBOOK_ALERTS_VERSION: '0.5.2'
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup Pages
         uses: actions/configure-pages@v5