[Model Card] standardize T2I Sdxl Lora model card

[cosmo3769]

What does this PR do?

Related issue: #6891 for T2I SDXL LoRA

Notebook link: test_model_card_template_t2i_sdxl_lora.ipynb

Generated model card link: test-model-card-template-t2i-sdxl-lora

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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• Did you write any new necessary tests?

Who can review?

@sayakpaul

[sayakpaul]

Looks awesome! Thanks so much for fixing the type annotations too!

[HuggingFaceDocBuilderDev]

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