Arctica greeter does not play well with accountsservice

[N0rbert]

Steps to reproduce:

1. Have Ubuntu MATE 20.10 installed
2. Install i3 with sudo apt-get install i3*
3. Reboot machine
4. Select i3 (or i3 with debug) on login screen

Expected results:

• i3 starts

Actual results:

• MATE starts instead of i3

---

Extra info:

After entering to "i3" it says:

$ sudo grep Session /var/lib/AccountsService/users/$USER
Session=mate
XSession=mate

After removing mate-session-manager it shows the following:

$ sudo grep Session /var/lib/AccountsService/users/$USER
Session=mate
XSession=i3

Downstream bug-report - https://bugs.launchpad.net/bugs/1910279 .

[N0rbert]

Still happens on latest Ubuntu MATE 22.04 LTS beta.