Bump postcss from 8.4.14 to 8.4.31 in /client

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.14 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@8.4.14...8.4.31)

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

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

client/package.json

@@ -41,7 +41,7 @@
     "has": "^1.0.3",
     "resolve": "^1.22.0",
     "rollup": "^2.74.1",
-    "postcss": "^8.4.14",
+    "postcss": "^8.4.31",
     "function-bind": "^1.1.1",
     "path-parse": "^1.0.7",
     "source-map-js": "^1.0.2",