ci: use tox for cirrus builds

Moving to tox to use isolated buids to avoid some environment specific
dragons in relation to `poetry install` command. Today, the symlinks
will cause issues when poetry attempts to add an editable install into
the venv due to a pathlib2 bug.

.cirrus.yml

@@ -16,11 +16,9 @@ test_task:
     - pkg install -y git-lite $PYPACKAGE $SQLPACKAGE
   pip_script:
     - $PYTHON -m ensurepip
-    - $PYTHON -m pip install pip -U
-    - $PYTHON -m pip install poetry -U
-    - $PYTHON -m poetry config virtualenvs.in-project true
-  deps_script: $PYTHON -m poetry install
-  test_script: $PYTHON -m poetry run pytest -q --junitxml=junit.xml tests
+    - $PYTHON -m pip install -U pip tox poetry
+    - poetry config virtualenvs.in-project true
+  tox_script: $PYTHON -m tox -e py -- -q --junitxml=junit.xml tests
   on_failure:
     annotate_failure_artifacts:
       path: junit.xml