Tests: fix: test_relayd_working_directory fails as root

From the original bug report:

This test succeeds as user, but fails as root:
not ok 23 - Warning about missing write permission is present

    Failed test 'Warning about missing write permission is present'
    in tools/working-directory/test_relayd_working_directory:test_relayd_debug_permission() at line 182.

The warning does not trigger because root always has access.

Skip this test since the permission check will succeed and the relay
daemon won't produce the expected error message.

Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I4eb29958aaca78405e1fdd2392d73472af0d5912