Fix PHP unit test

Author: allie500

tests/php/classes/test-class-wc-rest-connect-shipping-label-controller.php

@@ -541,5 +541,7 @@ private function set_origin_address( $address = array() ) {
 	 */
 	private function set_destination_address( WC_Order $order, $address = array() ) {
 		$order->set_address( $address, 'shipping' );
+
+		$order->save(); // Required for WC 10.3+ HPOS compatibility
 	}
 }