Ignore pytest failure because of warnings

ignore-warnings-pytest.md

If you're trying to get pytest running for old packages you may encounter failures due to ResourceWarning or DeperactionWarning errors

Those can be easily resolved by executing pytest as follows:

pytest -v tests -W ignore::ResourceWarning -W ignore::DeprecationWarning

In your nixpkgs package that would be

checkPhase = ''
  pytest -v tests -W ignore::ResourceWarning -W ignore::DeprecationWarning
'';