Consider dropping the pytest-runner test dependency

[musicinmybrain]

• rfc3339-validator version: 0.1.4
• Python version: any
• Operating System: any

Description

The pytest-runner package is deprecated upstream. Its README now advises:

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.

This came up in a review of a proposed python-rfc3339-validator package for Fedora Linux.

What I Did

• Followed pytest-runner upstream’s advice (leaving the already-empty setup_requires for now).
• Verified I can still run the tests with tox.

I also tried to run the tests with pip install -r requirements_dev.txt followed by python -m pytest or pytest, but this didn’t work on Python 3.10 because of the old pinned versions in requirements_dev.txt. However, after pip install --upgrade pip tox coverage pytest hypothesis strict_rfc3339, I was able to run the tests this way too.

I will offer these suggested changes as a PR.

[naimetti]

This night I'm going to try to release all these changes. Thanks!