bump symfony to 5.4.21

adapt to the new EventDispatcher API
  - Symfony\Component\EventDispatcher => Symfony\Contracts\EventDispatcher
  - dispatch() arguments swap
  - execute() must return int

app/Console/ProjectActivityArchiveCommand.php

@@ -14,8 +14,9 @@ class ProjectActivityArchiveCommand extends BaseCommand
             ->setDescription('Remove project activities after one year');
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $this->projectActivityModel->cleanup(strtotime('-1 year'));
+        return 0;
     }
 }