Fix CI
This fix contains three parts:
- start with a docker image from scratch and clone all needed repositories (this is needed until the pdelab image is functional again)
- use
HybridTreePath
instead ofTreePath
- use pdelab's matrix free linear operator and richardson
Btw, to be honest, I'm surprised the pipelines passed, since in earlier commits there were also issues with the out-of-date version of vectorclass. Curiously, the mirror on gitlab does not contain the patch @dominic submitted to the github repository, which caused the error in earlier commits.