Bumps [postcss](https://github.com/postcss/postcss) from 8.4.19 to 8.4.20.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.19...8.4.20)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
  update-type: version-update:semver-patch
...
Signed-off-by: dependabot[bot] <support@github.com>