make sure position_ids are passed in for causal mask creation for gpt-oss
Author: winglian
Pull request: yes

# What does this PR do?

Packing won't work with gpt-oss since it doesn't respect the position ids. See https://github.com/huggingface/transformers/pull/39194

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Fixes # (issue)

@ArthurZucker @Cyrilvallez 

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Comments:
**[For maintainers]** Suggested jobs to run (before merge)

run-slow: gpt_oss

Indeed, needs to be upstreamed in modular as well!