Current tox versions do not like how testenv.passenv is set

[musicinmybrain]

Current tox versions do not seem to like how testenv.passenv is set in tox.ini. Using the system tox on Fedora Linux 38:

$ tox --version
4.4.12 from /usr/lib/python3.11/site-packages/tox/__init__.py
$ tox
py37-core: failed with pass_env values cannot contain whitespace, use comma to have multiple values in a single line, invalid values found 'TOXENV CI CODECOV_*'
[…]

There are more errors of that form for every tox environment, and everything fails fast.

If I make the recommended change from passenv = TOXENV CI CODECOV_* to passenv = TOXENV,CI,CODECOV_*, things work much better; I suspect the remaining failures are generally due to transient issues at httpbin.org.

PR to follow.