wayland: fix handling of non-discrete scroll events (#9548)

https://github.com/zed-industries/zed/pull/9103 broke touchpad scrolling
on Wayland
This PR correctly filters the `Axis` to handle all non-discrete scroll
events (see
https://wayland.app/protocols/wayland#wl_pointer:enum:axis_source)

Should fix https://github.com/zed-industries/zed/issues/9525

Release Notes:

- N/A