Fixing typo in gemma3 image_processor_fast and adding a small test

[Zebz13]

What does this PR do?

Removes typo present in Gemma3 Model's ImageProcessorFast.
Added 1 small test for the verification of the same.
Fixes #36739

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Did you write any new necessary tests?

PR Discussion - #36739
Added small test for Gemma3 model with do_pan_and_scan disabled.

Who can review?

@zucchini-nlp

[github-actions]

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[zucchini-nlp]

Thanks!