Rename trainer arg tokenizer to processing_class

[qgallouedec]

What does this PR do?

Fixes #2161

Ensure backward compatibility for DPO and SFT only

>>> from datasets import load_dataset
>>> from transformers import AutoModelForCausalLM, AutoTokenizer
>>> from trl import DPOConfig, DPOTrainer
>>> model = AutoModelForCausalLM.from_pretrained("Qwen/Qwen2.5-0.5B-Instruct")
>>> tokenizer = AutoTokenizer.from_pretrained("Qwen/Qwen2.5-0.5B-Instruct")
>>> dataset = load_dataset("trl-lib/Capybara-Preferences", split="train")
>>> training_args = DPOConfig(output_dir="Qwen2.5-0.5B-DPO")
>>> trainer = DPOTrainer(model=model, args=training_args, train_dataset=dataset, tokenizer=tokenizer)
/fsx/qgallouedec/miniconda3/envs/trl/lib/python3.11/site-packages/huggingface_hub/utils/_deprecation.py:101: FutureWarning: `tokenizer` is deprecated and will be removed in version 0.14.0 for `DPOTrainer.__init__`. Use `processing_class` instead.
  return f(*args, **kwargs)

TODO

• BCO
• CPO
• DPO
• GKD
• KTO
• Nash-MD
• Online DPO
• ORPO
• PPOv2
• Reward
• RLOO
• SFT
• XPO

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[alvarobartt]

I may be missing something but is this required? Cannot we just use self.processing_class?

[qgallouedec]

You're right. Same for args. It will probably need some refactoring in the future

[alvarobartt]

I've seen that in other places too so maybe there's a rationale that I don't see for that? Not sure, but sure we'll keep it in mind