Bump cssnano from 5.1.15 to 7.1.1 in /frontend/packages/build

Bumps [cssnano](https://github.com/cssnano/cssnano) from 5.1.15 to 7.1.1.
- [Release notes](https://github.com/cssnano/cssnano/releases)
- [Commits](https://github.com/cssnano/cssnano/compare/[email protected]@7.1.1)

---
updated-dependencies:
- dependency-name: cssnano
  dependency-version: 7.1.1
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

frontend/packages/build/package.json

@@ -14,7 +14,7 @@
     "clean-webpack-plugin": "^4.0.0",
     "compression-webpack-plugin": "^9.0.0",
     "copy-webpack-plugin": "^10.0.0",
-    "cssnano": "^5.0.2",
+    "cssnano": "^7.1.1",
     "dotenv-webpack": "^7.0.1",
     "fork-ts-checker-webpack-plugin": "^7",
     "html-webpack-plugin": "^5.4.0",