TaskTree: Fix calling the proper group handler on stop

Add tests for it.

Change-Id: Ibb04b21c217196c9bbf6761851f4e1a300139a8c
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/libs/solutions/tasking/tasktree.cpp

@@ -893,6 +893,7 @@ void TaskNode::stop()
 
     if (!m_task) {
         m_container.stop();
+        m_container.m_runtimeData->updateSuccessBit(false);
         m_container.invokeEndHandler();
         return;
     }