GitHub Fine-grained tokens not fully supported

The new fine-grained personal access tokens (currently in beta) are not
working, as PyGithub does not provide a way to detect what access we
effectively have (oauth_scopes is set to None).

config_defaults.yml

@@ -15,6 +15,7 @@ github:
     # Generate at https://github.com/settings/tokens
     # The token must have at least `public_repo` scope. Additionally,
     # - `write:org` is required to run github_plugin_teams.py
+    # Note: Fine-grained tokens are currently not supported
     token: null
 
     # Global teams in mantisbt-plugins org that should have access to

github_plugin_teams.py

@@ -84,7 +84,7 @@ def main():
                 break
     if not has_required_privilege:
         print("""
-ERROR: This script requires a Token with the 'write:org' scope.
+ERROR: This script requires a Classic Token with the 'write:org' scope.
 
 Please update the config.yml file and GitHub Token as appropriate
 https://github.com/settings/tokens