Add null check to canRun method in CancelStaleWorkflowCronJob

Ensure the canRun method in CancelStaleWorkflowCronJob returns true when the cron job execution is null. This change includes updating the corresponding test case to cover the new behavior.

src/Bundle/ChillMainBundle/Tests/Services/Workflow/CancelStaleWorkflowCronJobTest.php

@@ -104,6 +104,11 @@ class CancelStaleWorkflowCronJobTest extends TestCase
             (new CronJobExecution('last-canceled-workflow-id'))->setLastEnd(new \DateTimeImmutable('2023-12-31 00:00:01', new \DateTimeZone('+00:00'))),
             false,
         ];
+
+        yield [
+            null,
+            true
+        ];
     }
 
     private function buildMessageBus(bool $expectDispatchAtLeastOnce = false): MessageBusInterface