update typo in bnb quantisation 4bit flag docstring

[hbraith]

What does this PR do?

Current stable (v11.1.0) docs at https://huggingface.co/docs/accelerate/v1.11.0/en/package_reference/utilities#accelerate.utils.BnbQuantizationConfig reference the 4 bit quantisation flag as load_in_4_bit instead of load_in_4bit as in the class constructor, example code, and transformers.BitsAndBytesConfig.

Note that the source code expects and uses load_in_4bit in the actual constructor, and the only reference I found matching load_in_4_bit was in the docstring for BnBQuantizationConfig in src/accelerate/utils/dataclasses.py.

Very minor change, but hoping to save others a quick moment of of puzzle, initially was confused as to why the transformers.BitsAndBytesConfig would have subtly different named kwargs, but turned out to be a non issue, as the underlying kwargs I was relying on were actually the same.

I thought it would be easier to raise a PR than an issue, but let me know if this was inappropriate.

I haven't run the tests as changes were only in the docstring, but did verify parsing via python -m compileall src/accelerate/utils/dataclasses.py and also ran make style without issues.

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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Tagging from the suggested list,

• Documentation/Maintained example: @SunMarc, @zach-huggingface

Thanks, let me know if I have missed anything, appreciate the work you all do!

[SunMarc]

Indeed thanks

[HuggingFaceDocBuilderDev]

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