Convert error to warning for logging without a Trainer

[carmocca]

What does this PR do?

Part of #8509

See:

#8509 (comment)
#8509 (comment)

Does your PR introduce any breaking changes? If yes, please list them.

None

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[carmocca]

cc @alanhdu @lucmos

[tchaton]

LGTM !

[ananthsub]

thanks for this!