Do not run tests in parallel on GIthub CI to try and avoid OOM situation

.github/workflows/ci.yml

@@ -34,6 +34,10 @@ jobs:
                 sudo apt-get update
                 sudo apt-get install openmpi-bin libopenmpi-dev
                 CONDA_ENVIRONMENT=.test-conda-env-py3.yml
+                
+                # https://github.com/inducer/grudge/pull/19
+                CISUPPORT_PARALLEL_PYTEST=no
+                
                 curl -L -O -k https://gitlab.tiker.net/inducer/ci-support/raw/master/build-and-test-py-project-within-miniconda.sh
                 . ./build-and-test-py-project-within-miniconda.sh