Use pytest instead of py.test

tox.ini

@@ -37,7 +37,7 @@ deps =
   django32: Django~=3.2.0
   django42: Django~=4.2.0
 commands =
-  py.test -s tests \
+  pytest -s tests \
    --junitxml=reports/junit.xml \
    --cov --cov-report xml:reports/coverage-{envname}.xml \
    {posargs}