fix: packages/site/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-ASTRO-14235580

Author: snyk-bot

packages/site/package.json

@@ -13,8 +13,8 @@
     "init:docs": "patternfly-doc-core init"
   },
   "dependencies": {
-    "@patternfly/patternfly-doc-core": "^1.15.3",
-    "astro": "^5.15.9"
+    "@patternfly/patternfly-doc-core": "^1.15.5",
+    "astro": "^5.16.3"
   },
   "devDependencies": {
     "tsx": "^4.19.0"