[bugfix][ci] try running python on ubuntu.

.gitlab-ci.yml

@@ -33,12 +33,9 @@ debian-11-gcc-9-17:
   variables:
     DUNECI_TOOLCHAIN:  gcc-9-17
 
-    #ubuntu:20.04--gcc:
-    #image: duneci/ubuntu:18.04
-    #script:
-    #- source /duneci/modules/dune-pip/bin/activate
-    #  # issue with setup-dunepy: dune-fem-dg not yet build so dependency in dune-fem-dg fails
-    #  # - python /duneci/modules/dune-python/bin/setup-dunepy.py --opts=$CI_PROJECT_DIR/scripts/opts/ci-gcc.opts install
-    #- duneci-standard-test
-    #variables:
-    #DUNECI_TOOLCHAIN:  gcc-7-17
+ubuntu-20.04-gcc-9-17:
+  image: registry.dune-project.org/docker/ci/ubuntu:20.04
+  script:
+    - duneci-standard-test
+  variables:
+    DUNECI_TOOLCHAIN:  gcc-9-17