/tmp/TailsToaster is too small for current Tails Installer

Originally created by @intrigeri on #14695 (Redmine)

See tails#8860 (comment 80901) and https://jenkins.tails.boum.org/view/Tails_ISO/job/test_Tails_ISO_feature-8860-tails-installer-improvements/3/cucumberTestReport/. I don’t understand why: the change that would logically impact this (tails#12705 (closed)) did not break the test suite for space-related reasons, and now tails#8860 (closed) does while I see no change in there that would obviously cause this problem. I suspect another, unrelated change (kernel upgrade or something) combined with tails#12705 (closed) broke this but we didn’t notice as tails#8860 (closed) broke the test suite earlier. Whatever, I’ll give that partition more space.

Edited May 15, 2020 by intrigeri