affected root keys returns wrong type when SetOrdered is involved

affected root keys returns wrong type when SetOrdered is involved: a task in harbor-swesmith-rl-artifacts: Harbor SWE-Smith 强化学习数据产物 (Harbor dataset). The affected root keys property returns a list instead of a set when dealing with SetOrdered objects in the diff tree. This breaks consistency…

The task

The `affected_root_keys` property returns a list instead of a set when dealing with SetOrdered objects in the diff tree. This breaks consistency since the method should always return a set.

Part of keryszhan/harbor-swesmith-rl-artifacts.