LYNX-308:Calculate discount for multicoupon

Author: wip44850

app/code/Magento/SalesRule/Model/Quote/Discount.php

@@ -330,7 +330,7 @@ public function fetch(Quote $quote, Total $total)
      * @param AddressInterface $address
      * @return void
      */
-    private function aggregateDiscountPerRule(
+    protected function aggregateDiscountPerRule(
         AbstractItem $item,
         AddressInterface $address
     ) {