GetSessionByPID DBUS call always fails on newer systemd versions

GetSessionByPID returns this error:

Error org.freedesktop.login1.NoSessionForPID: PID 2469 does not belong to any known session

So instead we will get session by calling GetSession("auto"). Tested on Fedora, should also work on openSUSE & KDE Neon.

BUG: 433408