Remove deprecated pytest-runner dependency

[penguinpee]

The pytest-runner project has been deprecated since 2019 and has been archived on git hub in December 2024.

This removes the dependency on the deprecated package and also removes deprecated keywords from setup.py related to it.

Use the new extra to install test dependencies in CI workflow.

[penguinpee]

For the deprecation notice of pytest-runner see:

https://github.com/pytest-dev/pytest-runner/commit/78a492cb9f611a4fccaf6556c966b848885833ba

For the removed/replaced deprecated keywords see:

https://setuptools.pypa.io/en/stable/references/keywords.html

[achilleas-k]

We're going to have to install pytest on appveyor for the tests.

[coveralls]

coverage: 78.615%. remained the same when pulling e0ba5cc58377e7c78fd1e48a2a5b317c50bf6e68 on penguinpee:drop_tests_require into 5e5ec01f0662d20b380301a187702cd11012fb3c on G-Node:master.