I think the issue is intent. It's fine if two voices happen to be similar. But it becomes a problem if you're explicitly trying to mimic someone's likeness in a way that is not obviously fair use (eg parody). If they reached out to Johansson first and then explicitly attempted to mimic her despite her refusal, it might be a problem. If the other voice was chosen first, and had nothing to do with sounding the same as Johansson, they should be fine.