chore(deps-dev): bump @types/react from 18.2.20 to 18.2.21 in /testsite

Bumps [@types/react](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/react) from 18.2.20 to 18.2.21.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/react)

---
updated-dependencies:
- dependency-name: "@types/react"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

testsite/package.json

@@ -30,7 +30,7 @@
   "devDependencies": {
     "@docusaurus/module-type-aliases": "3.0.0-alpha.0",
     "@docusaurus/tsconfig": "3.0.0-alpha.0",
-    "@types/react": "^18.2.20",
+    "@types/react": "^18.2.21",
     "@types/react-dom": "^18.2.7",
     "typescript": "^5.1.6"
   },