Bump postcss from 8.4.17 to 8.4.31

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.17 to 8.4.31.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](https://github.com/postcss/postcss/compare/8.4.17...8.4.31)

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

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

package.json

@@ -24,7 +24,7 @@
     "mdx-bundler": "^8.0.0",
     "next": "^13.4.6",
     "next-themes": "^0.0.14",
-    "postcss": "^8.4.5",
+    "postcss": "^8.4.31",
     "preact": "^10.6.2",
     "react": "^18.2.0",
     "react-dom": "^18.2.0",