sanity-check: make user-id run id as uid user, as was intended

Otherwise it's just a pointless duplicate of system-id.

Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D3649

common/sanity-check

@@ -38,7 +38,7 @@ common/run-test-in-systemd --name=user-env --user=user common/sanity-check-env u
 
 id || fail lava-id
 common/run-test-in-systemd --name=system-id id || :
-common/run-test-in-systemd --name=user-id id || :
+common/run-test-in-systemd --name=user-id --user=user id || :
 
 test -S /run/dbus/system_bus_socket || fail system-bus-is-up
 test -d /run/user/$(id -u user)/systemd || fail user-session-is-up