Fix paligemma warning message

[hiyouga]

What does this PR do?

Fixes hiyouga/LLaMA-Factory#6499

The logger.warning_once method only accepts one argument, so we remove the comma.

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Who can review?

@zucchini-nlp

[LysandreJik]

LGTM, thanks a lot for the PR and fix @hiyouga!