Release: v1.4

[qgallouedec]

What does this PR do?

Fixes # (issue)

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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Note

Low Risk
Low risk: only updates release/version metadata and the CI workflow’s checked-out release ref, with no runtime code changes.

Overview
Prepares the v1.4 release by updating project version metadata: sets VERSION to 1.4.0 (from 1.4.0.dev0) and bumps CITATION.cff version to 1.4.

Updates the tests_latest GitHub Actions workflow to checkout v1.4-release instead of v1.3-release when running the nightly “latest release” test job.

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[HuggingFaceDocBuilderDev]

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