[deepspeed zero3] need `generate(synced_gpus=True, ...)` (#22242)
* [deepspeed zero3] need generate(synced_gpus=True, ...)
* fix
* rework per Sylvain's suggestion
* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
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Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>