Bump postcss from 8.4.5 to 8.4.31 in /docs (#6762)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.5 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@8.4.5...8.4.31)

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

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docs/package.json

@@ -19,7 +19,7 @@
   "dependencies": {
     "ansi-regex": ">=6.0.1",
     "autoprefixer": "^10.4.2",
-    "postcss": ">=8.2.13",
+    "postcss": ">=8.4.31",
     "postcss-cli": "^9.1.0"
   }
 }