build(deps): bump postcss and react-scripts in /frontend

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.38 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 7.0.36 to 8.4.38
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@7.0.36...8.4.38)

Updates `react-scripts` from 4.0.3 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-4.x.md)
- [Commits](https://github.com/facebook/create-react-app/commits/[email protected]/packages/react-scripts)

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

Signed-off-by: dependabot[bot] <[email protected]>