from_pipe: Keep existing dtype by default

[missionfloyd]

What does this PR do?

Fixes a regression introduced in #10816, causing from_pipe to convert pipelines to float32 by default.

Fixes #12754

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?

@yiyixuxu @asomoza

[HuggingFaceDocBuilderDev]

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