Bump postcss and web-ext

Bumps [postcss](https://github.com/postcss/postcss) to 8.4.32 and updates ancestor dependency [web-ext](https://github.com/mozilla/web-ext). These dependencies need to be updated together.


Updates `postcss` from 8.4.23 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@8.4.23...8.4.32)

Updates `web-ext` from 7.6.2 to 7.9.0
- [Release notes](https://github.com/mozilla/web-ext/releases)
- [Commits](mozilla/web-ext@7.6.2...7.9.0)

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

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