Use constant over int. refs symfony#14648

Author: OskarStark

console/lockable_trait.rst

@@ -38,8 +38,8 @@ that adds two convenient methods to lock and release commands::
             // if not released explicitly, Symfony releases the lock
             // automatically when the execution of the command ends
             $this->release();
-            
-            return 0;
+
+            return Command:SUCCESS;
         }
     }