Fix dependencies & bail on first error

.github/dodona-image.dockerfile

@@ -1,12 +1,12 @@
 # Inherit from the Docker image for Dodona.
-FROM dodona/dodona-tested
+FROM tested-v2
 
 # Go back to being root.
 USER root
 WORKDIR /
 
 # Install some additional dependencies needed for testing.
-RUN pip install --no-cache-dir --upgrade pytest pytest-mock pytest-xdist
+RUN pip install --no-cache-dir --upgrade pytest pytest-mock pytest-xdist jinja2 marko
 
 # The source of the judge is available in TESTED_SOURCE.
-CMD pytest -n auto ${TESTED_SOURCE}/tests/
+CMD pytest -x -n auto ${TESTED_SOURCE}/tests/