The biggest problem on that front (assuming the former is not true) is Altman's tweets, but court-wise that's defensible (though I retract what I had here previously - probably not easily) as a reference to the general concept of the movie.
Because otherwise the situation you have is OpenAI seeking a particular style, hiring someone who can provide it, not trying to pass it off as that person (give or take the Tweet's) and the intended result effectively being: "random voice actress, you sound too much like an already rich and famous person. Good luck having no more work in your profession" - which would be the actual outcome.
The question entirely hinges on, did they include any data at all which includes ScarJo's voice samples in the training. And also whether it actually does sound similar enough - Frito-Lay went down because of intent and similarity. There's the hilarious outcome here that the act of trying to contact ScarJo is the actual problem they had.
EDIT 2: Of note also - to have a case, they actually have to show reputational harm. Of course on that front, the entire problem might also be Altman. Continuing the trend I suppose of billionaires not shutting up on Twitter being the main source of their legal issues.