authentication: run modernize for python3

rhodecode/authentication/routes.py

@@ -1,5 +1,3 @@
-
-
 # Copyright (C) 2012-2023 RhodeCode GmbH
 #
 # This program is free software: you can redistribute it and/or modify
@@ -121,7 +119,7 @@ class AuthnRootResource(AuthnResourceBase):
             counter = 1
             current = name
             while current in self._store.keys():
-                current = '{}{}'.format(name, counter)
+                current = f'{name}{counter}'
                 counter += 1
                 if counter > limit:
                     raise ConfigurationError(