Ensure that test notebook is destroyed after the end of its test

Don't let wxNotebook created in the recently added test for the events
generated when adding pages to it continue to live after the test end as
this breaks the subsequent tests using wxUIActionSimulator (but only
when using MinGW, for some reason).

tests/controls/notebooktest.cpp

@@ -20,6 +20,7 @@
 #endif // WX_PRECOMP
 
 #include "wx/notebook.h"
+#include "wx/scopedptr.h"
 
 #include "bookctrlbasetest.h"
 #include "testableframe.h"
@@ -125,6 +126,7 @@ TEST_CASE("wxNotebook::AddPageEvents", "[wxNotebook][AddPage][event]")
     wxNotebook* const
         notebook = new wxNotebook(wxTheApp->GetTopWindow(), wxID_ANY,
                                   wxDefaultPosition, wxSize(400, 200));
+    wxScopedPtr<wxNotebook> cleanup(notebook);
 
     CHECK( notebook->GetSelection() == wxNOT_FOUND );