gtk4: Scroll wheel events aren't handled properly in some sites

[aperezdc]

Some sites use mouse scroll wheel events for things other than scrolling the page, like zooming images or maps, but the latter does not work when using the gtk4 platform (x11 and wl work correctly, I didn't test drm).

The easiest way to reproduce is opening openstreetmap.org and using the mouse scroll wheel while hovering the map: it should zoom, but it doesn't.