[libkworkspace] Interim fix for the logout issue

Calls to a DBus activated service can fail if the sender quits whilst
the service is spawning
(https://gitlab.freedesktop.org/dbus/dbus/-/issues/72) and using
dbus-daemon.

This is a lazy interim fix that just makes these calls block as proper
fixes will require more work.

BUG: 432460


(cherry picked from commit 81d61861)