tests: Use longer timeout for client tests
The client-tests need about 90s on my arm64 hardware so 120s (instead of the default 30s) looks save while not being too long in case of a deadlock.
EDIT: Current tests are already close to the 30s timeout on gitlab as well: https://gitlab.gnome.org/GNOME/geary/-/jobs/1174936
Edited by Guido Günther