gsocketclient-slow test is flaky

Seen at least one failure of it on an unrelated test run.

Relevant except from the logs:

171/254 glib:gio / gsocketclient-slow           FAIL     1.66 s (killed by signal 6 SIGABRT)

--- command ---
G_TEST_BUILDDIR='/builds/GNOME/glib/_build/gio/tests' G_TEST_SRCDIR='/builds/GNOME/glib/gio/tests' GIO_LAUNCH_DESKTOP='/builds/GNOME/glib/_build/gio/gio-launch-desktop' GIO_MODULE_DIR='' LD_PRELOAD='/builds/GNOME/glib/_build/gio/tests/slow-connect-preload.so' /builds/GNOME/glib/_build/gio/tests/gsocketclient-slow --tap
--- stdout ---
# random seed: R02S26ae108cc39cbefb7d5005ff0eb8912c
1..1
# Start of socket-client tests
# GLib-GIO-DEBUG: IPv6 DNS error: Error resolving ?localhost?: Name or service not known
(/builds/GNOME/glib/_build/gio/tests/gsocketclient-slow:6317): GLib-GIO-DEBUG: 15:14:12.185: IPv6 DNS error: Error resolving ?localhost?: Name or service not known
Bail out! GLib-GIO:ERROR:../gio/tests/gsocketclient-slow.c:30:on_connected: assertion failed (error == NULL): Error resolving ?localhost?: Name or service not known (g-resolver-error-quark, 0)
--- stderr ---
**
GLib-GIO:ERROR:../gio/tests/gsocketclient-slow.c:30:on_connected: assertion failed (error == NULL): Error resolving ?localhost?: Name or service not known (g-resolver-error-quark, 0)