get_repo_license: allow GitHub's IP not permitted error

[bayandin]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

---

Continuation of #15909:

• Catch AuthenticationFailedError in get_repo_license as well.

Tested it by adding to def self.open_rest

raise AuthenticationFailedError.new(
  :env_token,
  "Although you appear to have the correct authorization credentials, the `Shopify` organization has an IP allow list enabled, and your IP address is not permitted to access this resource.",
)

and running brew audit --online --new-formula toxiproxy (from Homebrew/homebrew-core#140255)

[MikeMcQuaid]

Nice work, thanks again!