fix: upgrade autoprefixer from 10.4.19 to 10.4.20 (#397)

Snyk has created this PR to upgrade autoprefixer from 10.4.19 to 10.4.20.

See this package in npm:
https://www.npmjs.com/package/autoprefixer

See this project in Snyk:
https://app.snyk.io/org/vol/project/51ac37f4-1df0-4a49-8583-c3a498ab3573?utm_source=github&utm_medium=referral&page=upgrade-pr

Co-authored-by: snyk-bot <snyk-bot@snyk.io>
Co-authored-by: Andrew Newton <andy.newton@dvsa.gov.uk>

app/cdn/package.json

@@ -14,7 +14,7 @@
   ],
   "dependencies": {
     "@dvsa/cookie-manager": "^1.0.*",
-    "autoprefixer": "^10.4.19",
+    "autoprefixer": "^10.4.20",
     "chosen-npm": "^1.4.2",
     "govuk-frontend": "^5.4.1",
     "jquery": "^3.7.1",