Render only eligible adjustments on the order page

https://github.com/openfoodfoundation/openfoodnetwork/issues/3477

The admin orders edit form was displaying adjustments even if they were
"not eligible". For example, an additional fee with amount `0` is not
eligible. They were already hidden in the adjustments view and we are
hiding them in reports.

app/views/spree/admin/orders/_form.html.haml

@@ -5,7 +5,7 @@
   = render :partial => "spree/admin/orders/shipment", :collection => @order.shipments, :locals => { :order => order }
 
   = render :partial => "spree/admin/orders/_form/adjustments", :locals => { :adjustments => @order.price_adjustments, :order => order, :title => Spree.t(:line_item_adjustments)}
-  = render :partial => "spree/admin/orders/_form/adjustments", :locals => { :adjustments => @order.adjustments, :order => order, :title => Spree.t(:order_adjustments)}
+  = render :partial => "spree/admin/orders/_form/adjustments", :locals => { :adjustments => @order.adjustments.eligible, :order => order, :title => Spree.t(:order_adjustments)}
 
   - if order.line_items.exists?
     %fieldset#order-total.no-border-bottom{"data-hook" => "order_details_total"}

spec/features/admin/orders_spec.rb

@@ -283,6 +283,19 @@ feature %q{
         end
       end
 
+      scenario "shows only eligible adjustments" do
+        adjustment = create(
+          :adjustment,
+          adjustable: @order,
+          label: "invalid adjustment",
+          amount: 0
+        )
+
+        visit spree.edit_admin_order_path(@order)
+
+        expect(page).to have_no_content adjustment.label
+      end
+
       scenario "cannot split the order in different stock locations" do
         # There's only 1 stock location in OFN, so the split functionality that comes with spree should be hidden
         expect(page).to_not have_selector '.split-item'