Bump cssnano from 5.1.0 to 7.0.6

Bumps [cssnano](https://github.com/cssnano/cssnano) from 5.1.0 to 7.0.6.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/[email protected]@7.0.6)

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

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