Test suite: deal with GNOME's status menu not opening.

Since Bullseye we have the issue that clicking the status menu button
doesn't always open the menu, generally around 3 attempts are needed.

Interestingly, it doesn't matter if I click using Dogtail (the mouse
event is generated inside the system under testing) and xdotool (the
mouse event comes through virt-viewer from the host). And it seems
impossible to reproduce manually; even when I take over TailsToaster
and manually click I cannot reproduce.