Path in org.xfce.power.policy does not match the executable realpath, preventing it from work with upstream polkit

polkit > 126 will use realpath to check against the pkexec executable path https://github.com/polkit-org/polkit/issues/194

org.freedesktop.policykit.exec.path is set as /usr/sbin/xfce4-pm-helper, and it will fail as the real one is /usr/bin/xfce4-pm-helper