[BUGFIX] Catch __PHP_Incomplete_Class classes

Resolves: #66587
Releases: master, 8.7
Change-Id: I444c818e9f81d3595ca68513800c85d9f993f9b4
Reviewed-on: https://review.typo3.org/55685


Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/scheduler/Classes/Scheduler.php

@@ -434,7 +434,7 @@ class Scheduler implements \TYPO3\CMS\Core\SingletonInterface
      */
     public function isValidTaskObject($task)
     {
-        return $task instanceof Task\AbstractTask;
+        return get_class($task->getExecution()) !== '__PHP_Incomplete_Class' && $task instanceof Task\AbstractTask;
     }
 
     /**