gtk4: Disable int-conversion warning as error

This helps builds on 32bit machines when using GCC-14
there is a bug filed for fixing this in code [1]

[1] https://gitlab.gnome.org/GNOME/gtk/-/issues/6033


Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 3735b556)
Signed-off-by: Steve Sakoman <steve@sakoman.com>