Fix support for PHP8 union types

Author: nicolas-grekas

ServiceLocatorTrait.php

@@ -87,7 +87,7 @@ public function getProvidedServices(): array
                 } else {
                     $type = (new \ReflectionFunction($factory))->getReturnType();
 
-                    $this->providedTypes[$name] = $type ? ($type->allowsNull() ? '?' : '').$type->getName() : '?';
+                    $this->providedTypes[$name] = $type ? ($type->allowsNull() ? '?' : '').($type instanceof \ReflectionNamedType ? $type->getName() : $type) : '?';
                 }
             }
         }

ServiceSubscriberTrait.php

@@ -40,7 +40,7 @@ public static function getSubscribedServices(): array
             }
 
             if (self::class === $method->getDeclaringClass()->name && ($returnType = $method->getReturnType()) && !$returnType->isBuiltin()) {
-                $services[self::class.'::'.$method->name] = '?'.$returnType->getName();
+                $services[self::class.'::'.$method->name] = '?'.($returnType instanceof \ReflectionNamedType ? $returnType->getName() : $type);
             }
         }