reflect max_new_tokens in `Seq2SeqTrainer` (#18786)
reflect max_new_tokens in `Seq2SeqTrainer` (#18786)

* reflect max_new_tokens in gen_kwargs to `trainer.generate()`

* reflect max_new_tokens in `Seq2SeqTrainer`

* remove unnecessary variable

* Trigger CI

* fix style
huggingface/transformers,huggingface/transformers,huggingface/transformers,huggingface/transformers