Fix the syntax to satisfy PHP 7.3

Author: Oleg Namaka

src/Symfony/Component/Messenger/Bridge/Amqp/Tests/Transport/AmqpTransportTest.php

@@ -59,7 +59,7 @@ public function testReceivesMessagesInBlockingMode()
             $connection = $this->getMockBuilder(Connection::class)
                 ->disableOriginalConstructor()
                 ->onlyMethods(['getQueueNames', 'pull'])
-                ->getMock(),
+                ->getMock()
         );
 
         $decodedMessage = new DummyMessage('Decoded.');