tp_debug_client_get_messages_finish: fix annotation
tp_debug_client_get_messages_finish: fix annotation

Returning a GPtrArray with (transfer full) means the caller is expected
to do the equivalent of:

    g_ptr_array_foreach (pa, (GFunc) g_free, NULL);
    g_ptr_array_unref (pa);

whereas we just want them to unref it. This crashed my g-i-based
debug-client.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=65518
Reviewed-by: Guillaume Desmottes <f16649c7afcd84e3350287183c4ed23cb1aea57c@collabora.co.uk>

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib