fix: upgrade postcss from 8.4.18 to 8.4.34

Snyk has created this PR to upgrade postcss from 8.4.18 to 8.4.34.

See this package in npm:
https://www.npmjs.com/package/postcss

See this project in Snyk:
https://app.snyk.io/org/neutron-A49X5tRU3kb2nVTZv6t7SQ/project/13bf98cb-12db-4e0d-81b5-1836c5f26d9e?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot

docs/package-lock.json

@@ -26,7 +26,7 @@
     "@you54f/theme-github-codeblock": "^0.1.1",
     "autoprefixer": "^10.4.13",
     "clsx": "^1.2.1",
-    "postcss": "^8.4.18",
+    "postcss": "^8.4.34",
     "postcss-import": "^15.0.0",
     "prism-react-renderer": "^1.3.5",
     "react": "^17.0.2",