Bump cssnano from 5.1.15 to 9.2.2

Bumps [cssnano](https://github.com/cssnano/cssnano) from 5.1.15 to 9.2.2.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/cssnano@5.1.15...cssnano@9.2.2)

---
updated-dependencies:
- dependency-name: cssnano
  dependency-version: 9.2.2
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

package.json

@@ -14,7 +14,7 @@
     "autoprefixer": "^10.4.0",
     "bootstrap": "^5.3.8",
     "clipboard": "^2.0.8",
-    "cssnano": "^5.0.13",
+    "cssnano": "^9.2.2",
     "easymde": "^2.21.0",
     "fullcalendar": "^5.10.1",
     "gulp-concat": "^2.6.1",