tests: Fix wrong return type in test_int64_callback()
tests: Fix wrong return type in test_int64_callback()

https://bugzilla.gnome.org/show_bug.cgi?id=684700

davibe/pygobject,sfeltman/pygobject,pexip/pygobject,GNOME/pygobject,davibe/pygobject,sfeltman/pygobject,sfeltman/pygobject,pexip/pygobject,davibe/pygobject,davibe/pygobject,GNOME/pygobject,GNOME/pygobject,pexip/pygobject