build(deps-dev): Bump autoprefixer from 10.4.20 to 10.4.21 in /docs

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 10.4.20 to 10.4.21.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/main/CHANGELOG.md)
- [Commits](postcss/autoprefixer@10.4.20...10.4.21)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

docs/package-lock.json

@@ -1,6 +1,6 @@
 {
   "devDependencies": {
-    "autoprefixer": "^10.4.20",
+    "autoprefixer": "^10.4.21",
     "postcss-cli": "^11.0.0"
   }
 }