[TASK] Fix php8 array key in Scheduler Migration

Classes/Updates/MigrateSchedulerTasks.php

@@ -79,7 +79,7 @@ class MigrateSchedulerTasks implements UpgradeWizardInterface {
 		foreach ($tasks as $_task) {
 			$task = unserialize($_task['serialized_task_object'], [\__PHP_Incomplete_Class::class]);
 			$taskVars = $this->cleanArrayKeys((array)$task);
-			$identifier = $taskVars['*commandIdentifier'];
+			$identifier = $taskVars['*commandIdentifier'] ?? '';
 			if (
 				$identifier === 'sg_news:migratenews:runmigratenews'
 			) {