chore(deps-dev): bump postcss in /site in the all group (#825)

Bumps the all group in /site with 1 update: [postcss](https://github.com/postcss/postcss).


Updates `postcss` from 8.5.10 to 8.5.12
- [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/8.5.10...8.5.12)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.12
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: all
...

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