Fix typo in Speech2TextForConditionalGeneration example

[will-rice]

What does this PR do?

This PR fixes a small typo in the example docstring.

Fixes # (issue)

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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?

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@patil-suraj

[patil-suraj]

Thank you for fixing this!