Bump postcss from 8.4.22 to 8.4.23 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.22 to 8.4.23.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.22...8.4.23)

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

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

frontend/package.json

@@ -15,7 +15,7 @@
   },
   "devDependencies": {
     "autoprefixer": "10.4.14",
-    "postcss": "8.4.22",
+    "postcss": "8.4.23",
     "prettier": "2.8.8",
     "prettier-plugin-tailwindcss": "0.2.7",
     "tailwindcss": "3.3.1",