Fix invites form path (#5861)

app/views/invites/_form.html.haml

@@ -1,4 +1,4 @@
-= simple_form_for(@invite) do |f|
+= simple_form_for(@invite, url: controller.is_a?(Admin::InvitesController) ? admin_invites_path : invites_path) do |f|
   = render 'shared/error_messages', object: @invite
 
   .fields-group