Tiny typos in gemma2_modular.py after flex_attention introduction
Author: MekkCyber
Pull request: yes

# What does this PR do?
Fixing small typos in `modular_gemma2.py`
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## Before submitting
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## Who can review?

@ArthurZucker 

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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_34828). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

Actually flex attention now works as default so closing!