[Community Pipeline] Fix typo that cause error on regional prompting pipeline

[cjkangme]

What does this PR do?

Fixes #9874 (comment)

Hi
I apologize for the issue.
There's a bug in my code where an error occurs when prompts is a str and negative_prompts is a list due to a typo I made.
I've fixed the affected line.

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[a-r-r-o-w]

thanks for the fix and contributing this pipeline!

[HuggingFaceDocBuilderDev]

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