[generation] Fix misleading synced_gpus warning in continuous batching (#47158)
* [generation] Fix misleading synced_gpus warning in continuous batching
Correct the warning negation when synced_gpus is passed in continuous batching generation mode. Since synced_gpus is ignored and not processed, the warning should read 'is ignored' instead of 'is not ignored'.
Add a regression test in test_continuous_batching.py to verify.
* Remove regression test per maintainer review feedback
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Co-authored-by: Rémi Ouazan <83456801+remi-or@users.noreply.github.com>