Cast enum/bitfield values to gint/guint for sys tests
Cast enum/bitfield values to gint/guint for sys tests

GLib assumes that these are gint/guint internally so sign differences
don't really make a difference here, but cause test failures otherwise.

Fixes https://github.com/gtk-rs/gir/issues/572

EPashkin/gir,EPashkin/gir,GuillaumeGomez/gir,GuillaumeGomez/gir,gtk-rs/gir,GuillaumeGomez/gir,gtk-rs/gir,gtk-rs/gir