Minor changes to the new build system.
I tried the new system, e.g. recreated my dev setup with the current develop. A few small things came up in the process. See review threads.
The old module-image for the shared runners will be discontinued on October 31. All users still referencing gitlab-registry.mpcdf.mpg.de/mpcdf/module-image in their CI pipelines need to switch to the new CI images now, see instructions here.
I tried the new system, e.g. recreated my dev setup with the current develop. A few small things came up in the process. See review threads.