Update dependency undici to v6.21.2 [SECURITY]

Author: renovate[bot]

package.json

@@ -31,7 +31,7 @@
     "eslint-plugin-qwik": "^1.2.11",
     "prettier": "3.5.3",
     "typescript": "5.8.2",
-    "undici": "6.3.0",
+    "undici": "6.21.2",
     "vite": "5.4.15",
     "vite-tsconfig-paths": "5.1.4"
   }