Fix support for PHP8 union types

Author: nicolas-grekas

DependencyInjection/RegisterListenersPass.php

@@ -138,7 +138,7 @@ private function getEventFromTypeDeclaration(ContainerBuilder $container, string
             || !($r = $container->getReflectionClass($class, false))
             || !$r->hasMethod($method)
             || 1 > ($m = $r->getMethod($method))->getNumberOfParameters()
-            || !($type = $m->getParameters()[0]->getType())
+            || !($type = $m->getParameters()[0]->getType()) instanceof \ReflectionNamedType
             || $type->isBuiltin()
             || Event::class === ($name = $type->getName())
             || LegacyEvent::class === $name