chore: bump autoprefixer from 10.4.20 to 10.4.21 in /frontend/extension (#402)

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-version: 10.4.21
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

frontend/extension/package.json

@@ -30,7 +30,7 @@
     "@types/react-dom": "^18.3.1",
     "@typescript-eslint/eslint-plugin": "^7.18.0",
     "@typescript-eslint/parser": "^7.18.0",
-    "autoprefixer": "^10.4.20",
+    "autoprefixer": "^10.4.21",
     "eslint": "^8.57.1",
     "eslint-config-prettier": "^9.1.0",
     "eslint-plugin-prettier": "^5.2.5",