github/api: update personal access token format.

https://github.blog/changelog/2021-03-04-authentication-token-format-updates/

Library/Homebrew/utils/github/api.rb

@@ -21,6 +21,7 @@ module GitHub
         #{ALL_SCOPES_URL}
       #{Utils::Shell.set_variable_in_profile("HOMEBREW_GITHUB_API_TOKEN", "your_token_here")}
   EOS
+  GITHUB_PAT_REGEX = /^(?:[a-f0-9]{40}|gp1_[A-Za-z0-9_]{40,255})$/.freeze
 
   # Helper functions to access the GitHub API.
   #
@@ -127,7 +128,7 @@ module GitHub
       # Don't use passwords from the keychain unless they look like
       # GitHub Personal Access Tokens:
       #   https://github.com/Homebrew/brew/issues/6862#issuecomment-572610344
-      return unless /^[a-f0-9]{40}$/i.match?(github_password)
+      return unless GITHUB_PAT_REGEX.match?(github_password)
 
       github_password
     rescue Errno::EPIPE