don't register SchedulerTriggerNormalizer without symfony/serializer

Author: xabbuh

DependencyInjection/FrameworkExtension.php

@@ -2297,7 +2297,7 @@ private function registerSchedulerConfiguration(ContainerBuilder $container, Php
         }
 
         // BC layer Scheduler < 7.3
-        if (!class_exists(SchedulerTriggerNormalizer::class)) {
+        if (!ContainerBuilder::willBeAvailable('symfony/serializer', DenormalizerInterface::class, ['symfony/framework-bundle', 'symfony/scheduler']) || !class_exists(SchedulerTriggerNormalizer::class)) {
             $container->removeDefinition('serializer.normalizer.scheduler_trigger');
         }
     }