mod: run pytest w/ --color=yes in github actions

.github/workflows/pythonapp.yml

@@ -62,6 +62,7 @@ jobs:
       run: >
         pytest -v
         --cov=pysisyphus --cov-config .coveragerc --cov-report xml --cov-report term
+        --color yes
         --show-capture=no
         --durations=0
         -m "not benchmark and not skip_ci"