autotests: Fix testScreens

Currently, the test doesn't pass due to Xwayland encountering a protocol
error.

That protocol error occurs because the xdg-output is destroyed before
the wl_output.

This change moves the ownership of the xdg-output to wl-output so they
are destroyed together.

src/waylandoutput.cpp

@@ -92,7 +92,7 @@ WaylandOutput::WaylandOutput(AbstractWaylandOutput *output, QObject *parent)
     : QObject(parent)
     , m_platformOutput(output)
     , m_waylandOutput(new KWaylandServer::OutputInterface(waylandServer()->display()))
-    , m_xdgOutputV1(waylandServer()->xdgOutputManagerV1()->createXdgOutput(m_waylandOutput.data(), this))
+    , m_xdgOutputV1(waylandServer()->xdgOutputManagerV1()->createXdgOutput(m_waylandOutput.data(), m_waylandOutput.data()))
 {
     const QRect geometry = m_platformOutput->geometry();