Bump cssnano from 6.1.2 to 7.0.0 (#5024)

Bumps [cssnano](https://github.com/cssnano/cssnano) from 6.1.2 to 7.0.0.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/cssnano@6.1.2...cssnano@7.0.0)

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

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

Author: dependabot[bot]

Diff for: {{cookiecutter.project_slug}}/package.json

@@ -12,7 +12,7 @@
     "css-loader": "^6.5.1",
     "gulp-concat": "^2.6.1",
     "concurrently": "^8.0.1",
-    "cssnano": "^6.0.0",
+    "cssnano": "^7.0.0",
     "gulp": "^4.0.2",
     "gulp-imagemin": "^7.1.0",
     "gulp-plumber": "^1.2.1",