test(select-input): improve the test coverage of selectInput (#6230)

* test(select-input): improve the test coverage of selectInput

* test(select-input): refactor and enhance test cases for SelectInput component

* test(select-input): add unit tests for useSingle, useMultiple, and useOverlayInnerStyle hooks

* test(select-input): add unit tests for useSingle hooks

Author: RSS1102