Bump webpack-dev-server from 5.0.4 to 5.2.1 in /demo

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 5.0.4 to 5.2.1.
- [Release notes](https://github.com/webpack/webpack-dev-server/releases)
- [Changelog](https://github.com/webpack/webpack-dev-server/blob/master/CHANGELOG.md)
- [Commits](webpack/webpack-dev-server@v5.0.4...v5.2.1)

---
updated-dependencies:
- dependency-name: webpack-dev-server
  dependency-version: 5.2.1
  dependency-type: direct:development
...

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

Author: dependabot[bot]

demo/package.json

@@ -11,6 +11,6 @@
     "html-webpack-plugin": "^5.5.1",
     "webpack": "^5.94.0",
     "webpack-cli": "^5.1.1",
-    "webpack-dev-server": "^5.0.4"
+    "webpack-dev-server": "^5.2.1"
   }
 }