selectInput(selectize=FALSE) requires a `form-select` class

[daattali]

This might belong in the shiny repo.

When creating a selectInput() with selectize=FALSE in bootstrap 5, the resulting input does not have a chevron arrow on the side that makes it clear this is an openable box. See screenshot. This makes it appear as a text input.

The input needs to add class="form-select" to appear correctly in bs5.