Bump postcss from 8.4.23 to 8.4.31 in /assets (#194)

Bumps [postcss](https://github.com/postcss/postcss) from 8.4.23 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@8.4.23...8.4.31)

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

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assets/package.json

@@ -30,7 +30,7 @@
     "jest-environment-jsdom": "^29.4.3",
     "mini-css-extract-plugin": "^2.7.2",
     "normalize-scss": "^7.0.1",
-    "postcss": "^8.4.21",
+    "postcss": "^8.4.31",
     "postcss-loader": "^7.2.4",
     "postcss-scss": "^4.0.6",
     "postcss-url": "^10.1.3",