Bump postcss from 8.5.1 to 8.5.3 in /doc (#3318)

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.1 to 8.5.3.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.1...8.5.3)

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

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Author: dependabot[bot]

doc/package-lock.json

@@ -1,7 +1,7 @@
 {
   "devDependencies": {
     "autoprefixer": "^10.4.0",
-    "postcss": "^8.5.1",
+    "postcss": "^8.5.3",
     "postcss-cli": "^11.0.0"
   }
 }