Fix the test that was broken by #16445 rather than deleting it

Since the counter cache was properly being updated, the model became
stale. Simply reloading the model before attempting to destroy is
sufficient for this case. I believe this is enough of an edge case to be
a valid change to the tests, even though it represents a potential
breaking change.

activerecord/test/cases/locking_test.rb

@@ -263,6 +263,18 @@ def test_update_without_attributes_does_not_only_update_lock_version
     end
   end
 
+  def test_polymorphic_destroy_with_dependencies_and_lock_version
+    car = Car.create!
+
+    assert_difference 'car.wheels.count'  do
+      car.wheels << Wheel.create!
+    end
+    assert_difference 'car.wheels.count', -1  do
+      car.reload.destroy
+    end
+    assert car.destroyed?
+  end
+
   def test_removing_has_and_belongs_to_many_associations_upon_destroy
     p = RichPerson.create! first_name: 'Jon'
     p.treasures.create!