Update dependency astro to v6 [SECURITY]

Author: renovate[bot]

website/package.json

@@ -10,7 +10,7 @@
   },
   "dependencies": {
     "@astrojs/starlight": "^0.37.0",
-    "astro": "^5.6.1",
+    "astro": "^6.0.0",
     "sharp": "^0.34.0",
     "starlight-links-validator": "^0.19.0",
     "starlight-versions": "^0.7.0"