Unpin diffusers and pass onnx exporters tests

[IlyasMoutawwakil]

What does this PR do?

There are also problems with modernbert making the CI red because it's still released in transformers.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

[HuggingFaceDocBuilderDev]

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[echarlaix]

LGTM, thanks a lot @IlyasMoutawwakil

[xenova]

Thanks @IlyasMoutawwakil 👍 For modernbert, is this something we can fix with

MIN_TRANSFORMERS_VERSION = version.parse("4.48.0")

?

[IlyasMoutawwakil]

oh yes apparently we can thanks to
https://github.com/huggingface/optimum/blob/c46de055049acc550eca1ff96414b2aba3a95dee/tests/exporters/onnx/test_onnx_export.py#L212-L216C
thanks for the catch, fixing it in a second