Set datasets temporary upper version 2.20.0

[albertvillanova]

What does this PR do?

This PR sets datasets temporary upper version to 2.20.0, so that the CI is fixed and it does not block other PRs.

Note that in the latest datasets release, a breaking change was introduced for security reasons: https://github.com/huggingface/datasets/releases/tag/2.20.0

Datasets with a Python loading script now require passing trust_remote_code=True to be used

• See discussion in: Implement SD3 loss weighting #8528 (comment)

This PR should be reverted once, the underlying issue (mandatory passing of trust_remote_code=True) is addressed.

CC: @sayakpaul

Fixes # (issue)

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[sayakpaul]

Cc: @asomoza @yiyixuxu

[albertvillanova]

Note that the CI error is unrelated: it is due to the release of numpy 2.0.0 made yesterday.

[lhoestq]

I merged https://huggingface.co/datasets/hf-internal-testing/fill10/discussions/1 to fix the CI, I believe we can close this PR

[sayakpaul]

Thanks