test: use systemd-run --wait in TEST-44-LOG-NAMESPACE
    
    The test appears to be occasionally failing. It uses systemd-run to echo
    'hello world' into a namespaced journal and then uses journalctl to look for it,
    but it doesn't wait.
    In the failed runs it can't find it, but the automated journal dump shows
    the message at the end.
    
    Use --wait to avoid races.
    
    (cherry picked from commit cf9844ffabd7fd51f22e729692b79d55cd7bdd76)