Bump immer and react-scripts in /examples/react-app

Bumps [immer](https://github.com/immerjs/immer) to 9.0.21 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 `immer` from 8.0.1 to 9.0.21
- [Release notes](https://github.com/immerjs/immer/releases)
- [Commits](immerjs/immer@v8.0.1...v9.0.21)

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: immer
  dependency-type: indirect
- dependency-name: react-scripts
  dependency-type: direct:production
...

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