The shader self test uses GLRenderTarget and restores the viewport. Due
to the setVirtualScreenGeometry not being set the calculated viewport is
incorrect and any rendering breaks. This is a regression introduced with
1708278a451e6dab92549f9cabe6ad13ea3b4ba2 which only affects Wayland
backends which do not perform per screen rendering.
The glxbackend was not affected as it sets the viewport on screen
geometry change.