Only show one error for radio field and check boxes
Only show one error for radio field and check boxes

We don't currently have any radio fields or check boxes where it's
possible to get more than one validation error. However, since we
never want to show more than one error at a time for a field, this
changes the error messages for the relevant widgets to only show the
first error if there ever were multiple.

alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin