* libffi-dev is required for building jupyter
* matplotlib can not be installed using wheels on the used version of alpine
linux, which means it must be compiled and a large number of other packages
have to be installed as well.
This is very inefficient: see eg.
https://pythonspeed.com/articles/alpine-docker-python/
Apart from that, matplotlib is actually not required for rendering
notebook files in gitea and it will pull in other dependencies which take some
time to build (ie numpy).
Johan Van de Wauw