tests: Fix compilation of resolver-parsing test on FreeBSD
This fixes commit cdcb1798.
dn_comp()
is needed to build fake DNS records for most of the tests in
this file. The new ownership test is no exception.
See https://gitlab.gnome.org/GNOME/glib/-/jobs/4058481
Signed-off-by: Philip Withnall pwithnall@gnome.org