Remove pytest-runner from setup_requires

[walsvid]

Due to pytest-runner being in a deprecated state (as seen in references [1] [2]), it is recommended that the author clean up the dependency of imgcat on pytest-runner. Conflicts caused by this dependency can lead to incorrect installation issues during pip install.

[1] https://github.com/pytest-dev/pytest-runner/
[2] https://pypi.org/project/pytest-runner/

Deprecation Notice
pytest-runner depends on deprecated features of setuptools and relies on features that break security mechanisms in pip. For example ‘setup_requires’ and ‘tests_require’ bypass pip --require-hashes. See also pypa/setuptools#1684.

It is recommended that you:

Remove 'pytest-runner' from your setup_requires, preferably removing the setup_requires option.

Remove 'pytest' and any other testing requirements from tests_require, preferably removing the tests_requires option.

Select a tool to bootstrap and then run tests such as tox.