gio/tests: Use the right format specifier
gio/tests: Use the right format specifier

dev_t - the type of st_dev - is always 8 byte.
Use G_GUINT64_FORMAT to ensure 8 byte and thus not fail on i386.

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib