MistralCausalLMPreprocessor.from_preset docs mistakenly refer to BERT

[jeffcarp]

https://keras.io/keras_hub/api/models/mistral/mistral_causal_lm_preprocessor/#:~:text=a%20built%2Din,BertTextClassifierPreprocessor.from_preset().

[jeffcarp]

It appears this way because it's picking up the docstring from the base class.

keras-hub/keras_hub/src/models/preprocessor.py

Lines 145 to 148 in 5180e78

	1. a built-in preset identifier like `'bert_base_en'`
	2. a Kaggle Models handle like `'kaggle://user/bert/keras/bert_base_en'`
	3. a Hugging Face handle like `'hf://user/bert_base_en'`
	4. a path to a local preset directory like `'./bert_base_en'`

It's not reasonable to customize this docstring for each class just to change the model name.