Change potential inputs_embeds padding logger.warning to logger.warning_once

[naimenz]

What does this PR do?

This PR changes the warning for potential padding in embeddings from logger.warning to logger.warning_once

Fixes #30871

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@amyeroberts

[amyeroberts]

Thanks!

[amyeroberts]

@naimenz Could you rebase to include the recent changes on main? The datasets library had a recent release which is causing the failures on the CI runs for this PR. We pushed a commit #31417 which resolves this, but will need to be included on this branch to set up the right CI env

[naimenz]

Oh sure, rebased now! Thanks @amyeroberts