Hotfix CI: Mark tests as xfail with transformers dev for Llava models

[albertvillanova]

Hotfix CI: Mark tests as xfail with transformers dev for Llava models.

Hotfix for:

• CI fails with dev dependencies for Llava models: AssertionError: Param is not updated #5497

Pending of a fix upstream.

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Note

Low Risk
Low risk: only adjusts pytest expectations for CI by marking known-failing Llava/LlavaNext cases as xfail on transformers dev releases, with no production code changes.

Overview
Marks the Llava and LlavaNext vision-language model cases in test_train_vlm for both DPOTrainer and SFTTrainer as conditional xfail when running against transformers dev releases.

This prevents CI failures from a known upstream transformers 5.6.0.dev0 issue (see #5497) while keeping the tests strict for other versions.

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[HuggingFaceDocBuilderDev]

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[qgallouedec]

Thanks for the quick fix!