OO-4840: cancel timer of the task executor manager

src/main/java/org/olat/core/commons/services/taskexecutor/manager/TaskExecutorManagerImpl.java

@@ -112,6 +112,7 @@ public class TaskExecutorManagerImpl implements TaskExecutorManager {
 	}
 
 	public void shutdown() {
+		timer.cancel();
 		taskExecutor.shutdownNow();
 		sequentialTaskExecutor.shutdownNow();
 		lowPriorityTaskExecutor.shutdownNow();