fix: incorrect type for onChange handler argument

[ndom91]

Description

• Fix onChange argument type from ITimezone (which was a union between the full ITimezoneOption object and string) to ITimezoneOption only.

Since the value can be both a string (i.e. Europe/Berlin) or the full ITimezoneOption object, that's okay, but after going through the component and coming out of the onChange function, so to speak, it'll always be the ITimezoneOption object. Never a string as an argument in onChange.

Linked Issues

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