build(deps-dev): bump postcss from 8.4.25 to 8.4.31 in /client

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.25 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.4.25...8.4.31)

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

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

client/package.json

@@ -39,7 +39,7 @@
     "eslint-plugin-react": "^7.20.6",
     "eslint-plugin-react-hooks": "^4.2.0",
     "parcel": "^2.0.0",
-    "postcss": "^8.4.4",
+    "postcss": "^8.4.31",
     "prettier": "^2.0.0",
     "process": "^0.11.10",
     "stylelint": "^15.10.1",