chore: bump cssnano from 4.1.11 to 6.0.2

Bumps [cssnano](https://github.com/cssnano/cssnano) from 4.1.11 to 6.0.2.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/v4.1.11...cssnano@6.0.2)

---
updated-dependencies:
- dependency-name: cssnano
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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