TaskTree: Add static assert ensuring the right Adapter type

Change-Id: I87e995151ec21963c5514dfdb1863cfd2bc457b9
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/libs/solutions/tasking/tasktree.h

@@ -318,6 +318,9 @@ class CustomTask : public GroupItem
 {
 public:
     using Task = typename Adapter::Type;
+    static_assert(std::is_base_of_v<TaskAdapter<Task>, Adapter>,
+                  "The Adapter type for the CustomTask<Adapter> needs to be derived from "
+                  "TaskAdapter<Task>.");
     using EndHandler = std::function<void(const Task &)>;
     static Adapter *createAdapter() { return new Adapter; }
     CustomTask() : GroupItem({&createAdapter}) {}