After duplicating variations, ensure the duplicated object is current

Fixes woocommerce#15770

includes/admin/class-wc-admin-duplicate-product.php

@@ -160,6 +160,9 @@ public function product_duplicate( $product ) {
 
 				$child_duplicate->save();
 			}
+
+			// Get new object to reflect new children.
+			$duplicate = wc_get_product( $duplicate->get_id() );
 		}
 
 		return $duplicate;