Forcing X11 doesn't work

[GiantBlargg]

Since #3011 forcing X11 with with_x11 doesn't work.

The problem is here:
https://github.com/rust-windowing/winit/blob/7541220a419f0e383251c37be574fef9fd5827e4/src/platform_impl/linux/mod.rs#L754C1-L764C10

#[cfg(wayland_platform)]
if attributes.forced_backend == Some(Backend::Wayland)
    || env::var("WAYLAND_DISPLAY").is_ok()
{
    return EventLoop::new_wayland_any_thread().map_err(Into::into);
}

#[cfg(x11_platform)]
if attributes.forced_backend == Some(Backend::X) || env::var("DISPLAY").is_ok() {
    return Ok(EventLoop::new_x11_any_thread().unwrap());
}

If WAYLAND_DISPLAY is set, X never gets the chance to force itself.