Thinking about that episode, I imagine the legal risk is less in trying to sound like Scarlett Johansson, and more in trying to sound like Samantha, the AI character in Her. Warner Brothers or Spike Jonze probably has some legal rights to the character, and an argument could be made that OpenAI was infringing on that. The viability of that argument probably depends on how much people conflate the two or believe that the one was meant to represent the other.