refac: docstrings in import_utils.py

[yijun-lee]

What does this PR do?

Fixes #9567

Before submitting

• 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?

@a-r-r-o-w @stevhliu

[a-r-r-o-w]

Thanks for the improvements!

[HuggingFaceDocBuilderDev]

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