Fix inhomogeneous shape error in example

[Zantares]

What does this PR do?

Fixes #30000 , which has reported an inhomogeneous shape error in the QA example with numpy >= 1.24.0:

batch = {k: np.array(v) for k, v in batch.items()} ValueError: setting an array element with a sequence. The requested array has an inhomogeneous shape after 2 dimensions. The detected shape was (64, 384) + inhomogeneous part.

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Who can review?

@sanchit-gandhi

[Zantares]

@ArthurZucker can you help to review this PR? Thanks!

[sanchit-gandhi]

Sorry for the delay, and thanks for the clean fix @Zantares! Just one core maintainer review required from @amyeroberts, then we'll get this PR merged!

[amyeroberts]

Thanks for fixing!