Update line_item spec to create a target_shipment for destroy test

This test is demonstrating a false passing because the OrderInventory
instance actually receives the `verify` message on being created, and
previous to this change, that would happen after the `expect_` line,
causing this test to pass despite `verify` not being received during
the `destory`. This change adds a `target_shipment` to the
`line_item`, which is needed to trigger the `verify` call.

core/spec/models/spree/line_item_spec.rb

@@ -5,6 +5,7 @@
 RSpec.describe Spree::LineItem, type: :model do
   let(:order) { create :order_with_line_items, line_items_count: 1 }
   let(:line_item) { order.line_items.first }
+  let(:target_shipment) { Spree::Shipment.new }
 
   context '#destroy' do
     it "fetches soft-deleted products" do
@@ -18,7 +19,8 @@
     end
 
     it "returns inventory when a line item is destroyed" do
-      expect_any_instance_of(Spree::OrderInventory).to receive(:verify)
+      line_item.target_shipment = target_shipment
+      expect_any_instance_of(Spree::OrderInventory).to receive(:verify).with(target_shipment)
       line_item.destroy
     end
 
@@ -30,8 +32,8 @@
   context "#save" do
     context "target_shipment is provided" do
       it "verifies inventory" do
-        line_item.target_shipment = Spree::Shipment.new
-        expect_any_instance_of(Spree::OrderInventory).to receive(:verify)
+        line_item.target_shipment = target_shipment
+        expect_any_instance_of(Spree::OrderInventory).to receive(:verify).with(target_shipment)
         line_item.save
       end
     end