Jamba - Skip 4d custom attention mask test

[amyeroberts]

What does this PR do?

Fixes failing test on main: https://app.circleci.com/pipelines/github/huggingface/transformers/92832/workflows/0cbde306-131c-479b-b938-bca2fb838a82/jobs/1215777

Applies the same fix as #30780

However, applying created another failing test: test_assisted_decoding_matches_greedy_search_0_random.

This fails because the model now has _supports_cache_class unset, but passes past_key_values as HybridMambaAttentionDynamicCache, which triggers an exception here.

Mamba doesn't have this issue, because it doesn't define any models in all_generative_models in its model tester, and so the generation tests "pass" but are in fact skipped.

The tests are skipped now, but we should update either the interaction between the cache and generation to ensure this isn't necessary. I've opened a related issue here #30828

cc @gante

[HuggingFaceDocBuilderDev]

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[ArthurZucker]

Thanks