nit(vertico): fix typo and docstring

[smallwat3r]

Fix a typo and add a missing function docstring in the vertico module.

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• [x] I searched the issue tracker and this hasn't been PRed before.
• [x] My changes are not on the do-not-PR list for this project.
• [x] My commits conform to the git conventions.

[hlissner]

Thanks for your help!