Fix referencing context initializers

With definition, that has been used instead of reference, container has
used to created 2 instances of initializer: one with service id, and one
"anonymous", described by spl_object_hash in a container, it breaked
stateful initializers: in my case initializer was also used to reset
state before next scenario/example, and initializing and resetting happened
with different instances of initializer

src/ServiceContainer/SymfonyExtension.php

@@ -182,7 +182,7 @@ final class SymfonyExtension implements Extension
     {
         $definition = $container->findDefinition('fob_symfony.environment_handler.context_service');
         foreach ($container->findTaggedServiceIds(ContextExtension::INITIALIZER_TAG) as $serviceId => $tags) {
-            $definition->addMethodCall('registerContextInitializer', [$container->getDefinition($serviceId)]);
+            $definition->addMethodCall('registerContextInitializer', [new Reference($serviceId)]);
         }
     }