It's not an impersonation it is the actor using their own natural voice.
"We believe that AI voices should not deliberately mimic a celebrity's distinctive voice — Sky's voice is not an imitation of Scarlett Johansson but belongs to a different professional actress using *her own natural speaking voice*"
>>franka+(OP)
With the law, it is often about intent. If OpenAI had the intent to make a voice that sounded like Scarlett Johansson's in her, then I think that might be problematic for OpenAI. I am not a lawyer though.