[Notifier] Add missing use statement

Author: OskarStark

Test/TransportFactoryTestCase.php

@@ -17,6 +17,7 @@
 use Symfony\Component\Notifier\Exception\UnsupportedSchemeException;
 use Symfony\Component\Notifier\Transport\Dsn;
 use Symfony\Component\Notifier\Transport\TransportFactoryInterface;
+use Symfony\Component\Notifier\Transport\TransportInterface;
 
 /**
  * A test case to ease testing a notifier transport factory.