Follow-up from "Saved configuration for issue board"

The following discussion from !2912 (merged) should be addressed:

• @MadLittleMods started a discussion: (+1 comment)

  When clicking the current milestone option in the dropdown to unselect it, it doesn't update in the dropdown or the selected value. This is a different behavior from the other dropdowns.

  

In a single-select dropdown, clicking the currently selected item should keep it selected.

For Issue Board Config, this includes Assignee, Weight and Milestone select fields.