Warm-start model fitting notebook crashes

Cell 5 of the [notebook](https://github.com/facebook/prophet/blob/main/notebooks/additional_topics.ipynb), where warm-start fitting happens, crashes with the following error: `AttributeError: 'list' object has no attribute 'tolist'`.

Prophet version is 1.1.1, and you can see full details in this StackOverflow [question](https://stackoverflow.com/questions/76818210/warm-start-fitting-of-prophet-model-crashes).