test: add workaround for networkd downgrade issue

test/units/TEST-88-UPGRADE.sh

@@ -83,6 +83,9 @@ timer2=$(systemctl show -P NextElapseUSecRealtime upgrade_timer_test.timer)
 
 dnf downgrade -y --allowerasing --disablerepo '*' "$pkgdir"/distro/*.rpm
 
+# FIXME: See https://github.com/systemd/systemd/pull/39293
+systemctl stop systemd-networkd-resolve-hook.socket || true
+
 # Some distros don't ship networkd, so the test will always fail
 if command -v networkctl >/dev/null; then
     networkd=1