chore(deps): bump postcss and detective-postcss

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


Updates `postcss` from 7.0.36 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@7.0.36...8.4.31)

Updates `detective-postcss` from 3.0.1 to 6.1.3
- [Release notes](https://github.com/dependents/node-detective-postcss/releases)
- [Commits](dependents/node-detective-postcss@v3.0.1...v6.1.3)

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

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