diffoscope suddenly needs a lot more /tmp space

This bug was originally reported by Holger Levsen (holger@debian.org) in Debian bug #981123:

Package: diffoscope
Version: 164
Severity: important

diffoscope 164 was released on the 8th of January 2021 and approx.
since the 10th of January /tmp on jenkins.debian.net has regularily
seen filling up as can be seen on:

https://jenkins.debian.net/munin/debian.net/jenkins.debian.net/df.html

and

https://jenkins.debian.net/munin/static/dynazoom.html?cgiurl_graph=3D/munin=
-cgi/munin-cgi-graph&plugin_name=3Ddebian.net/jenkins.debian.net/df&size_x=
=3D800&size_y=3D400&start_epoch=3D1608831726&stop_epoch=3D1611682926

even better and I do think the timing is relevant as there were no
other relevant changes to jenkins.debian.net those days.