Bump cssnano from 5.1.15 to 6.0.0 (#418)

Bumps [cssnano](https://github.com/cssnano/cssnano) from 5.1.15 to 6.0.0.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/[email protected]@6.0.0)

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

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

Author: dependabot[bot]

package.json

@@ -58,7 +58,7 @@
     "chai": "^4.0.0",
     "cross-env": "^7.0.3",
     "css-loader": "^6.7.3",
-    "cssnano": "^5.1.15",
+    "cssnano": "^6.0.0",
     "eslint": "^8.23.0",
     "eslint-config-takiyon-react": "^3.0.0",
     "eslint-import-resolver-webpack": "^0.13.0",