build(deps-dev): bump cssnano from 7.0.5 to 7.0.6 in /csfieldguide

Bumps [cssnano](https://github.com/cssnano/cssnano) from 7.0.5 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-patch
...

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

Author: dependabot[bot]