deps: bump postcss from 8.5.5 to 8.5.6 in the dependency-updates group

Bumps the dependency-updates group with 1 update: [postcss](https://github.com/postcss/postcss).


Updates `postcss` from 8.5.5 to 8.5.6
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.5...8.5.6)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: dependency-updates
...

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

Author: dependabot[bot]