tests: Port gdbus-threading to use g_assert_*() rather than g_assert()
tests: Port gdbus-threading to use g_assert_*() rather than g_assert()

g_assert() can be compiled out with G_DISABLE_ASSERT, which renders the
test rather useless.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

https://gitlab.gnome.org/GNOME/glib/issues/1515

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