Bump autoprefixer from 10.4.20 to 10.4.21 in /client

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] <support@github.com>

Author: dependabot[bot]

client/package-lock.json

@@ -40,7 +40,7 @@
         "@types/react": "^19.0.10",
         "@types/react-dom": "^19.0.4",
         "@vitejs/plugin-react-swc": "^3.5.0",
-        "autoprefixer": "^10.4.20",
+        "autoprefixer": "^10.4.21",
         "eslint": "^9.14.0",
         "eslint-config-prettier": "^9.1.0",
         "eslint-plugin-prettier": "^5.2.3",