Incorrect type hint of "exponential_decay_length_penalty" in function "generate"

[pohunghuang-nctu]

Hi,
Please check below line,

transformers/src/transformers/generation_utils.py

Line 956 in 7e7f62b

exponential_decay_length_penalty: Optional[Tuple[Union[int, float]]] = None,

According to doc string, "exponential_decay_length_penalty (tuple(int, float), optional, defaults to model.config.exponential_decay_length_penalty):" (https://github.com/huggingface/transformers/blob/main/src/transformers/generation_utils.py#L1114)

the correct type hint should be "Optional[Tuple[int, float]]", the number of tuple elements should be 2, and must be "int" in position 0, and "float" in position 1.