Update pytest-runner to 2.10.1

[pyup-bot]

There's a new version of pytest-runner available.
You are currently using 2.9. I have updated it to 2.10.1

These links might come in handy: PyPI | Changelog | Repo

Changelog

2.10.1

• 21: Avoid mutating dictionary keys during iteration.

2.10

• 20: Leverage technique in setuptools 794 <https://github.com/pypa/setuptools/issues/794>_
  to populate PYTHONPATH during test runs such that
  Python subprocesses will have a dependency context
  comparable to the test runner.

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖