[fix] sliding window attention mask (#38045)
* fix sliding attn
* make style
* Update tests/test_modeling_common.py
Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>
* no a second throught, should default to `True` fo BC
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Co-authored-by: Joao Gante <joaofranciscocardosogante@gmail.com>
