3491: Pull check into a function
3491: Pull check into a function

The code to check a radio button needs to be a bit more complex than
just `trigger('click')` because the order of the prop getting set and
the event handlers being fired doesn't match what happens when the user
clicks a radio button.

Authors: 8bac6c593a5a494fbcd5bb593fa691623bcdd932@lloydnye

alphagov/verify-frontend,alphagov/verify-frontend,alphagov/verify-frontend,alphagov/verify-frontend