Bump postcss from 8.5.3 to 8.5.4 in /doc (#3390)

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.3 to 8.5.4.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.3...8.5.4)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.4
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

doc/package-lock.json

@@ -1,7 +1,7 @@
 {
   "devDependencies": {
     "autoprefixer": "^10.4.21",
-    "postcss": "^8.5.3",
+    "postcss": "^8.5.4",
     "postcss-cli": "^11.0.1"
   }
 }