chore(deps-dev): bump postcss from 8.4.38 to 8.4.39 in /frontend

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.38 to 8.4.39.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.38...8.4.39)

---
updated-dependencies:
- dependency-name: postcss
  dependency-type: direct:development
...

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

Author: dependabot[bot]

frontend/package.json

@@ -53,7 +53,7 @@
     "css-loader": "^3.6.0",
     "dotenv-webpack": "^8.1.0",
     "html-webpack-plugin": "^5.6.0",
-    "postcss": "^8.4.38",
+    "postcss": "^8.4.39",
     "postcss-cli": "^11.0.0",
     "postcss-loader": "^8.1.1",
     "style-loader": "^4.0.0",