Fix typo in tox.ini

[dvora-h]

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Please provide a description of the change here.

[akx]

Please see #2395 and #2387...

[chayim]

Vote for closing, given how this will be handled in 5.0. WDYT?

[dvora-h]

Not relevant anymore (see #2793)