Fix local_files_only for checkpoints with shards

[hlky]

What does this PR do?

Discussed internally https://huggingface.slack.com/archives/C07S1S33BQD/p1734513644104739

Works if we just let huggingface_hub handle local_files_only. Also tested with the cases from #8913 and #8898

from huggingface_hub import snapshot_download
from diffusers import UNet2DConditionModel

ckpt_path = snapshot_download("hf-internal-testing/unet2d-sharded-dummy-subfolder")
loaded_model = UNet2DConditionModel.from_pretrained(ckpt_path, subfolder="unet", local_files_only=True)

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

cc @yiyixuxu

[HuggingFaceDocBuilderDev]

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[yiyixuxu]

thanks!