Speed up CI by using pre-built image?
In https://git.geomar.de/python/xorca_docker, I've built a docker image that contains all we need here. This https://git.geomar.de/python/xorca_mockup_nemo_data/blob/master/.gitlab-ci.yml shows how to use this image (and drop the then-obsolete package installation steps).
Result will be reduced job durations because the env is not built everytime a test is run.
(cc: @jan-klaus-rieck)