build(deps): bump postcss from 8.4.21 to 8.4.31 in /website

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.21 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@8.4.21...8.4.31)

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

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

website/package.json

@@ -1,7 +1,7 @@
 {
   "dependencies": {
     "autoprefixer": "^10.4.13",
-    "postcss": "^8.4.21",
+    "postcss": "^8.4.31",
     "postcss-cli": "^10.1.0"
   }
 }