Revert error to warning when loading LoRA from repo with multiple weights

[apolinario]

What does this PR do?

Reverts back from a raised error to a warning if a LoRA repository contains multiple *.safetensors files.

Pros:

1. Avoids applications breaking if a 3rd party does an action, scenario: a LoRA repo had a single LoRA, so the codebase works. Then, the LoRa repo author uploads a second LoRA to the repo. Now the app breaks due to the action of the 3rd party
2. More Hub-centric: users can just pass the Hub nicename of a LoRA without worrying too much about weight-names (not an obvious interaction on the Hub to get weight names)

I know there are pros and cons and I'm sure this has been discussed before. But this is such a simple PR that I just did it in case it's helpful. Feel free to reject/close if not aligned and happy to further discuss in case we can find some other solution.

Before submitting

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• Did you write any new necessary tests?

Who can review?

@yiyixuxu @sayakpaul @BenjaminBossan

[HuggingFaceDocBuilderDev]

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[sayakpaul]

I don't mind it.