[autotests/integration] Fix SceneQPainter::testWindowScaled

A code of line was missing.

autotests/integration/scene_qpainter_test.cpp

@@ -196,6 +196,7 @@ void SceneQPainterTest::testWindowScaled()
     KWin::Cursor::setPos(10, 10);
     // this test verifies that a window is rendered correctly
     using namespace KWayland::Client;
+    QVERIFY(Test::setupWaylandConnection(Test::AdditionalWaylandInterface::Seat));
     QVERIFY(Test::waitForWaylandPointer());
     QScopedPointer<Surface> s(Test::createSurface());
     QScopedPointer<ShellSurface> ss(Test::createShellSurface(s.data()));