make blank pytest.ini for abacusutils

tox.ini

@@ -338,6 +338,7 @@ commands_pre =
     pip install --no-build-isolation classy corrfunc
     pip install -e abacusutils[test]
     pip install -r {env_tmp_dir}/requirements.txt
+    bash -c "echo '' > pytest.ini"
     pip freeze
 commands =
     pytest abacusutils