Prevent users from closing Tails Upgrader while an upgrade is being applied
The current dialog when the upgrade is being applied has an "OK" button that, when clicked closes the dialog.
The upgrade is still being applied in the background: tails-upgrader is still running and the USB stick is flashing.
We should prevent people from closing this dialog until the upgrade is fully applied.
At this point, Tails is offline and we recommended people to close everything else. People click OK might wonder what should happen next and we won't display anything else before several minutes. I guess that a lot of people might restart in doubt of what's happening.
I guess that this is the root cause behind #14754.
Marking as Elevated as it might lead to a broken Tails.
But #16603 does not cover the (much more ambitious) "Prevent users from closing Tails Upgrader" part
FTR, segfault's branch for #16603 hides the "OK" button, which is great. But one can still close the dialog by pressing "ESC" (and possibly via the task bar, I did not check this) so we're not there yet.
Once this change is applied, do you think priority = Elevated is still deserved?