chore(deps): bump postcss and nuxt in /frontend

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.38 and updates ancestor dependency [nuxt](https://github.com/nuxt/nuxt/tree/HEAD/packages/nuxt). These dependencies need to be updated together.


Updates `postcss` from 7.0.39 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@7.0.39...8.4.38)

Updates `nuxt` from 2.15.8 to 2.17.3
- [Release notes](https://github.com/nuxt/nuxt/releases)
- [Commits](https://github.com/nuxt/nuxt/commits/v2.17.3/packages/nuxt)

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

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