Fix(Promotions): Return 200 on benefits#edit

In solidusio#5981, we accidentally set this error render to a response code 422.

promotions/lib/controllers/backend/solidus_promotions/admin/benefits_controller.rb

@@ -28,7 +28,7 @@ def edit
         if params.dig(:benefit, :calculator_type)
           @benefit.calculator_type = params[:benefit][:calculator_type]
         end
-        render layout: false, status: :unprocessable_entity
+        render layout: false
       end
 
       def update