[BUG] Avoid depdencies with URLs in setup.cfg

[abravalheri]

setuptools version

main: d212daa

Python version

Python 3.8

OS

Ubuntu 20.04.3 LTS

Additional environment information

No response

Description

It seems that #2865 might have accidentally introduced a kind of dependency that is not accepted by PyPi:

[options.extras_require]
testing =
        ...
-	pytest-virtualenv>=1.2.7
+	pytest-virtualenv @ git+https://github.com/jaraco/pytest-plugins@distutils-deprecated#subdirectory=pytest-virtualenv

in setup.cfg.

PyPI forbids uploading packages with dependencies outside of PyPI (via URLs specs).

Expected behavior

An alternative for this implementation is to leave the previous dependency as it was in setup.cfg, but overwrite it using the deps field in tox.ini.

How to Reproduce

This problem is currently being pointed out by the CI:
https://github.com/pypa/setuptools/runs/4196605393?check_suite_focus=true
To replicate the problem it is necessary to try to submit the distribution files to PyPI

Output

HTTPError: 400 Bad Request from https://upload.pypi.org/legacy/
Invalid value for requires_dist. Error: Can't have direct dependency: "pytest-virtualenv @ git+https://github.com/jaraco/pytest-plugins@distutils-deprecated#subdirectory=pytest-virtualenv ; extra == 'testing'"
ERROR: InvocationError for command /home/runner/work/setuptools/setuptools/.tox/release/bin/python -m twine upload 'dist/*' (exited with code 1)

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