[Fix] Update for Docker Images

Due to an update of the docker images minor changes are required for the CI

.gitlab-ci.yml

@@ -21,7 +21,7 @@ tests-and-coverage:
     - mkdir -p ~/.config/matplotlib
     - echo "backend:template" > ~/.config/matplotlib/matplotlibrc
     - mkdir public
-    - py.test -v -n $NUM_CORES --cov-report html --cov-report term --cov=. -m "not longrun" --html test-report/index.html --junitxml=report.xml
+    - py.test -v -n $NUM_CORES --cov-report html --cov-report xml --cov-report term --cov=. -m "not longrun" --html test-report/index.html --junitxml=report.xml
     - python3 -m coverage xml
   tags:
     - docker
@@ -109,7 +109,8 @@ ubuntu:
   before_script:
     - apt-get -y remove python3-sympy
     - ln -s /usr/include/locale.h /usr/include/xlocale.h
-    - pip3 install `grep -Eo 'sympy[>=]+[0-9\.]+' setup.py | sed 's/>/=/g'`
+    - pip3 install sympy==1.6
+    # - pip3 install `grep -Eo 'sympy[>=]+[0-9\.]+' setup.py | sed 's/>/=/g'`
     # - pip3 install `grep -Eo 'sympy[>=]+[0-9\.]+' setup.py | sed 's/>/=/g'`
   script:
     - export NUM_CORES=$(nproc --all)