Bump postcss and fomantic-ui in /web_src/fomantic

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.30 and updates ancestor dependency [fomantic-ui](https://github.com/fomantic/Fomantic-UI). These dependencies need to be updated together.


Updates `postcss` from 6.0.23 to 8.4.30
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@6.0.23...8.4.30)

Updates `fomantic-ui` from 2.8.7 to 2.9.3
- [Release notes](https://github.com/fomantic/Fomantic-UI/releases)
- [Commits](fomantic/Fomantic-UI@2.8.7...2.9.3)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: fomantic-ui
  dependency-type: direct:production
...

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