fix: Use selected for attendee order-form dropdowns (#4654)

Author: Haider8

app/templates/components/forms/orders/order-form.hbs

@@ -86,7 +86,7 @@
               {{else if (eq field.fieldIdentifier 'gender')}}
                 <UiDropdown
                   @class="search selection"
-                  @value={{mut (get holder field.fieldIdentifier)}}
+                  @selected={{get holder field.fieldIdentifier}}
                   @onChange={{action (mut holder.gender)}} as |execute mapper|>
                   <Input
                     @type="hidden"
@@ -104,7 +104,7 @@
               {{else if (eq field.fieldIdentifier 'country')}}
                 <UiDropdown
                   @class="search selection"
-                  @value={{mut (get holder field.fieldIdentifier)}}
+                  @selected={{get holder field.fieldIdentifier}}
                   @onChange={{action (mut holder.country)}} as |execute mapper|>
                   <Input
                     @type="hidden"
@@ -123,7 +123,7 @@
               {{else if (eq field.fieldIdentifier 'ageGroup')}}
                 <UiDropdown
                   @class="search selection"
-                  @value={{mut (get holder field.fieldIdentifier)}}
+                  @selected={{get holder field.fieldIdentifier}}
                   @onChange={{action (mut holder.ageGroup)}} as |execute mapper|>
                   <Input
                     @type="hidden"