* fix 8-bit serialization tests

* add more clarification

* Update src/transformers/quantizers/quantizer_bnb_8bit.py

Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

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Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>