Bump postcss and web-ext

Bumps [postcss](https://github.com/postcss/postcss) and [web-ext](https://github.com/mozilla/web-ext). These dependencies needed to be updated together.

Updates `postcss` from 8.4.29 to 8.4.32
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.29...8.4.32)

Updates `web-ext` from 7.8.0 to 7.9.0
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@7.8.0...7.9.0)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: indirect
- dependency-name: web-ext
  dependency-type: indirect
...

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

Author: dependabot[bot]