tests: Add a debug message to gdbus-peer test
tests: Add a debug message to gdbus-peer test

This might help diagnose the CI test failure here:
https://gitlab.gnome.org/GNOME/glib/-/jobs/8222

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>
Reviewed-by: nobody

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