Update tox to 3.25.0

[pyup-bot]

This PR updates tox from 3.24.5 to 3.25.0.

Changelog

3.25.0

--------------------

Bugfixes
^^^^^^^^

- Fixed failing isolated_build because setuptools warning was captured
in ``build_requires``. -- by :user:`zariiii9003`
`2332 <https://github.com/tox-dev/tox/issues/2332>`_
- Avoid potential 30s delay caused by socket.getfqdn(). -- by :user:`ssbarnea`
`2375 <https://github.com/tox-dev/tox/issues/2375>`_


Features
^^^^^^^^

- Ignore missing commands if they are prefixed by ``-``
-- by :user:`cdown`.
`2315 <https://github.com/tox-dev/tox/issues/2315>`_
- Add default environment variables (such as http_proxy) regardless of their case to passenv on UNIX -- by :user:`poggenhans`.
`2372 <https://github.com/tox-dev/tox/issues/2372>`_
- On Windows ``PROGRAMFILES``, ``PROGRAMFILES(X86)``, and ``PROGRAMDATA`` environment variables are now passed through, unmasking system values necessary to locate resources such as a C compiler.
`2382 <https://github.com/tox-dev/tox/issues/2382>`_


Documentation
^^^^^^^^^^^^^

- Deleted the tox mailing list -- by :user:`jugmac00`
`2364 <https://github.com/tox-dev/tox/issues/2364>`_

Links

• PyPI: https://pypi.org/project/tox
• Changelog: https://pyup.io/changelogs/tox/
• Docs: https://tox.readthedocs.io

[pyup-bot]

Closing this in favor of #261