[Single file] fix single file config loading when passing dicts.

[sayakpaul]

What does this PR do?

Fixes https://github.com/huggingface/diffusers/actions/runs/9055285304/job/24876182073#step:7:3821

[HuggingFaceDocBuilderDev]

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[yiyixuxu]

ohh thanks! :)
looks good to me but I'll wait for @DN6 to comment if there is any reason the dict was not supported here

I think if we decided to accept config as a dict we should also update the doc string
if for some reason, we decide to no longer acceptconfig as a dict we should deprecate it

[yiyixuxu]

also I thought we are moving all the single-file tests to the same place? are these tests intended to be kept there?

[sayakpaul]

Yeah, I think so too.

https://github.com/huggingface/diffusers/tree/main/tests/single_file has all the tests but I think we need to remove them from tests/models/unets/ and elsewhere.

[DN6]

Actually this test and functionality should be removed. We don't support configuring models via dict in from_pretrained so from_single_file shouldn't support it either. config should be a model repo id or a path to a local model repo. I'll update the test.

[sayakpaul]

Closing the PR then :)