[Trainer] Fix model name in push_to_hub
Author: sanchit-gandhi
Pull request: yes

# What does this PR do?

Trainer's `push_to_hub` fails if `model_name` is specified in the kwargs. 

The variable `model_name` is explicitly defined in the `push_to_hub` method:
https://github.com/huggingface/transformers/blob/d447c460b16626c656e4d7a9425f648fe69517b3/src/transformers/trainer.py#L3449

And then subsequently passed **alongside** the kwargs to the method `create_model_card`:
https://github.com/huggingface/transformers/blob/d447c460b16626c656e4d7a9425f648fe69517b3/src/transformers/trainer.py#L3471

This means if `model_name` is specified in the kwargs, it is passed **twice** to `create_model_card`, once from the variable and once from the kwargs, giving a `TypeError`:
```python
from transformers import Trainer, TrainingArguments, Wav2Vec2ForCTC

model = Wav2Vec2ForCTC.from_pretrained("hf-internal-testing/tiny-random-wav2vec2")
training_args = TrainingArguments(output_dir="dummy_dir_for_issue")
trainer = Trainer(args=training_args, model=model)
trainer.push_to_hub(model_name="pretty-model-name")
```

**Traceback**
```
File ~/transformers/src/transformers/trainer.py:3471, in Trainer.push_to_hub(self, commit_message, blocking, **kwargs)
   3469 # push separately the model card to be independant from the rest of the model
   3470 if self.args.should_save:
-> 3471     self.create_model_card(model_name=model_name, **kwargs)
   3472     try:
   3473         self.repo.push_to_hub(
   3474             commit_message="update model card README.md", blocking=blocking, auto_lfs_prune=True
   3475         )

TypeError: create_model_card() got multiple values for keyword argument 'model_name'
```

Fixes #20058.


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