Bump minimum SymPy version and add Python 3.9 to CI

Same as pystencils!208 (merged)

.gitlab-ci.yml

@@ -112,6 +112,7 @@ ubuntu:
       - $ENABLE_NIGHTLY_BUILDS
   image: i10git.cs.fau.de:5005/pycodegen/pycodegen/ubuntu
   script:
+    - export NUM_CORES=$(nproc --all)
     - pip3 install `grep -Eo 'sympy[>=]+[0-9\.]+' setup.py | sed 's/>/=/g'`
     - pip3 install `grep -Eo 'numpy[>=]+[0-9\.]+' setup.py | sed 's/>/=/g'`
     - mkdir -p ~/.config/matplotlib
@@ -119,7 +120,7 @@ ubuntu:
     - pip3 install git+https://gitlab-ci-token:${CI_JOB_TOKEN}@i10git.cs.fau.de/pycodegen/pystencils.git@master#egg=pystencils
     - env
     - pip3 list
-    - pytest-3 -v -m "not longrun" --junitxml=report.xml
+    - pytest-3 -v -n $NUM_CORES -m "not longrun" --junitxml=report.xml
   tags:
     - docker
     - cuda11