Minor Description
It seems we had the bad luck that our Dockerfile building/validation image got
broken because of a change in its upstream parent image openjdk:11 that was upgraded
to the latest version of its parent version (debian:stable). Debian stable does
not include Java 8 anymore, so when you build the image (as I did to validate
the release) it is broken.
We should fix this by installing Java 'manually' in the docker image. To avoid
this kind of breakages in the future we should only rely on a pinned OS image
and install all dev dependencies from there probably install Java.
There are also some additional warnings that it would be good to fix, e.g.
apt-utils and wheel in pip upgrade.