fix: docs/package.json & docs/yarn.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-ASTRO-15763371
- https://snyk.io/vuln/SNYK-JS-ASTROJSINTERNALHELPERS-15763364

Author: snyk-io[bot]

docs/package.json

@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@astrojs/starlight": "^0.31.0",
-    "astro": "^5.1.9",
+    "astro": "^6.0.0",
     "sharp": "^0.33.5"
   },
   "devDependencies": {