Bump postcss and react-scripts in /react-app

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.23 and updates ancestor dependency [react-scripts](https://github.com/facebook/create-react-app/tree/HEAD/packages/react-scripts). These dependencies need to be updated together.


Updates `postcss` from 7.0.21 to 8.4.23
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/7.0.21...8.4.23)

Updates `react-scripts` from 3.4.1 to 5.0.1
- [Release notes](https://github.com/facebook/create-react-app/releases)
- [Changelog](https://github.com/facebook/create-react-app/blob/main/CHANGELOG-3.x.md)
- [Commits](https://github.com/facebook/create-react-app/commits/react-scripts@5.0.1/packages/react-scripts)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: react-scripts
  dependency-type: direct:production
...

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

react-app/package.json

@@ -13,7 +13,7 @@
     "react": "^16.14.0",
     "react-bootstrap": "^1.5.2",
     "react-dom": "^16.14.0",
-    "react-scripts": "3.4.1",
+    "react-scripts": "5.0.1",
     "semantic-ui-css": "^2.4.1",
     "semantic-ui-react": "^2.0.3"
   },