Merge branch 'update-build' into 'master'

Update build

See merge request control/teaching/grt/notebooks!12

.gitlab-ci.yml

+
 test notebooks:
-  image: git.tu-berlin.de:5000/control/teaching/docker/cubert:pytest
+  image: git.tu-berlin.de:5000/control/teaching/docker/morbo:pytest
   tags:
     - docker
   script:
-    - pytest --nbmake --nbmake-timeout=900 --junitxml junitReport.xml -n=8 *.ipynb
+    - pytest --nbmake --nbmake-timeout=900 --junitxml junitReport.xml --numprocesses=4 *.ipynb
   retry: 1
   artifacts:
     when: always