chore: update dependency cssnano to v6 (#45)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package.json

@@ -46,7 +46,7 @@
     "@typescript-eslint/eslint-plugin": "^6.21.0",
     "@typescript-eslint/parser": "^6.21.0",
     "autoprefixer": "^10.4.9",
-    "cssnano": "^5.1.13",
+    "cssnano": "^6.0.0",
     "eslint": "^8.57.0",
     "eslint-config-airbnb": "^19.0.4",
     "eslint-config-airbnb-typescript": "^17.1.0",