tests test tests, not code

The test put a reference to the XCB::Window as data
to the _net_wm_transient property, not the window ID
This "works" (you get various garbage transients for
the leader in addition) as long as the window id itself
is the first item in the structure (because that is what
the test resolves to verify what it has done) bug fails
when the XCB::Window structure changes and anything
is the first item (or, btw., when the compiler feels
to re-align the structure and adds some padding...)

So let's fix the test by at least passing the proper
data reference.

is FIXED-IN: 5.4.1
REVIEW: 124888
also see REVIEW: 124864

autotests/test_xcb_wrapper.cpp

@@ -298,7 +298,8 @@ void TestXcbWrapper::testTransientFor()
 
     // Create a Window with a transient for hint
     Window transientWindow(createWindow());
-    transientWindow.changeProperty(XCB_ATOM_WM_TRANSIENT_FOR, XCB_ATOM_WINDOW, 32, 1, &m_testWindow);
+    xcb_window_t testWindowId = m_testWindow;
+    transientWindow.changeProperty(XCB_ATOM_WM_TRANSIENT_FOR, XCB_ATOM_WINDOW, 32, 1, &testWindowId);
 
     // let's get another transient object
     TransientFor realTransient(transientWindow);