lomiri: logout should always log you out

How to reproduce this issue:

• Install Debian 13 minimal on physical hardware (e.g. a notebook) or a VM, and run apt install lomiri. Reboot.
• Login into Lomiri
• start some apps, as if you have been using Lomiri for some time
• Go to the system/session indicator (most right indicator) and log out of Lomiri

What you will observe:

• Sometimes you end up in the lomiri-greeter again, so that's good, after logging in again, you get a new session (no apps running)
• Sometimes you get a new session immediately instead of being sent to the greeter
• This issue is not 100% reproducible, but ~50%

What should happen:

• Logging out should always send you back to the lomiri-greeter / lightdm and require a new/fresh login