changed MllamaPreTrainedModel._prepare_4d_causal_attention_mask
Author: AndriiZelenko
Pull request: yes

## Resolves Issue https://github.com/huggingface/transformers/issues/35918#issue-2814092472, for detailed info please refer to issue, that one documented well 

# What does this PR do?

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Fixes [# (issue)](https://github.com/huggingface/transformers/issues/35918#issue-2814092472)


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Comments:
Hi @AndriiZelenko, I believe this is already being fixed in a larger PR here: https://github.com/huggingface/transformers/pull/35763