[FIX] mail_environment: default computation

fix the implementation of _compute_default_authentication
to match what is expected by the mixin

mail_environment/models/ir_mail_server.py

@@ -27,7 +27,7 @@ def _server_env_fields(self):
         return mail_fields
 
     def _compute_default_authentication(self):
-        return "login"
+        self.update({"smtp_authentication": "login"})
 
     @api.model
     def _server_env_global_section_name(self):