Bump cssnano from 7.1.7 to 7.1.8 (#4045)

Bumps [cssnano](https://github.com/cssnano/cssnano) from 7.1.7 to 7.1.8.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/cssnano@7.1.7...cssnano@7.1.8)

---
updated-dependencies:
- dependency-name: cssnano
  dependency-version: 7.1.8
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]