Add FIXME for coupon spec failure

Ran out of time so added this to fix next time.

Author: Kendra Riga

promotions/spec/models/solidus_promotions/promotion_handler/coupon_spec.rb

@@ -400,6 +400,10 @@ def expect_adjustment_creation(adjustable:, promotion:)
       end
 
       it "successfully removes the coupon code from the order" do
+        # FIXME:
+        # If we call `order.recalcualte` the test will pass.
+        # But we think there are better ways to test this assertion, such as
+        # that the adjustments have changed.
         subject.remove
         expect(subject.error).to eq nil
         expect(subject.success).to eq "The coupon code was successfully removed from this order."