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

Author: renovate[bot]

.github/workflows/astro.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Setup Bun
         uses: oven-sh/setup-bun@v2