Bump postcss from 8.5.8 to 8.5.9 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.8 to 8.5.9.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.8...8.5.9)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.9
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

frontend/package-lock.json

@@ -27,7 +27,7 @@
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.5.2",
     "globals": "^17.4.0",
-    "postcss": "^8.5.8",
+    "postcss": "^8.5.9",
     "tailwindcss": "^3.4.19",
     "typescript": "~6.0.2",
     "typescript-eslint": "^8.58.0",