build(deps): bump postcss and nuxt

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.31 and updates ancestor dependency [nuxt](https://github.com/nuxt/nuxt). These dependencies need to be updated together.


Updates `postcss` from 8.4.21 to 8.4.31
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.21...8.4.31)

Updates `nuxt` from 2.16.1 to 3.7.4
- [Release notes](https://github.com/nuxt/nuxt/releases)
- [Commits](nuxt/nuxt@v2.16.1...v3.7.4)

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

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