Fix deprecation warning

[rpkilby]

No description provided.

[pelme]

Hmm, is there any chance we could have our own test suite catch any pytest warnings and fail? We should never ship a version that gives pytest-warnings.

I have not seen this warning myself in pytest-django itself or in my own project, where does it show up?

[rpkilby]

I found this while fixing deprecation warnings for DRF. Running their test suite w/ the -Wonce flag generates this warning as well as the one from #393.

[rpkilby]

Hmm, is there any chance we could have our own test suite catch any pytest warnings and fail? We should never ship a version that gives pytest-warnings.

I was able to view errors w/ python -Wonce -m pytest. You could try to force errors w/ -Werror, but I was getting errors from other dependencies.

[blueyed]

See also https://github.com/fschulze/pytest-warnings.

[pelme]

Thanks for this PR! I've opened a new issue to track catching warnings in our CI setup: #415