Fix docstring mismatch in GenAIGenerativeModelHook

[jeff3071]

Summary

Change docstring train_dataset to training_dataset in GenAIGenerativeModelHook.supervised_fine_tuning_train .

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Was generative AI tooling used to co-author this PR?

• Yes (GPT 5.6 sol)

Generated-by: [GPT 5.6 sol] following the guidelines

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