Manifest v3 script-src exceptions not working?

In the "Migrating to Manifest v3" article, it says that the directives, one of them being script-src, may have "only the following values" which then goes on to list "self" however I used that in my code and I still got the error " 'content_security_policy.extension_pages': Insecure CSP value "https://js.pusher.com/4.2/pusher.min.js" in directive 'script-src'."

{
  "manifest_version": 3,
  "name": "Real-time NFL score",
  "version": "1.0",
  "description": "A simple Chrome extension to simulate the NFL scores in real-time",
  "content_security_policy": {
  "extension_pages": "script-src 'self' https://js.pusher.com/4.2/pusher.min.js https://stats.pusher.com; object-src 'self'"
  },
  "action": {
    "default_icon": "./img/icon.png",
    "default_popup": "popup.html"
  },
  "permissions": ["notifications", "activeTab"]
}