[DI] Fix private-by-default BC layer

Author: nicolas-grekas

Tests/DependencyInjection/FrameworkExtensionTest.php

@@ -953,6 +953,7 @@ public function testEventDispatcherService()
         $this->loadFromFile($container, 'default_config');
         $container
             ->register('foo', \stdClass::class)
+            ->setPublic(true)
             ->setProperty('dispatcher', new Reference('event_dispatcher'));
         $container->compile();
         $this->assertInstanceOf(EventDispatcherInterface::class, $container->get('foo')->dispatcher);