Fix CI

[mauritsvanrees]

• A new version of black introduced minor changes.
• Test with latests Zope 4/5 versions.
• Fix tox to let Python 3.9 test Zope 5 only. On GitHub Actions, Zope 5 is tested on a few more Python versions. Locally this fixes an error that makes no sense:

ERROR: Cannot install plone-recipe-zope2instance[test]==6.10.3.dev0
because these package versions have conflicting dependencies.

The conflict is caused by:
    plone-recipe-zope2instance[test] 6.10.3.dev0 depends on Zope>=4.0b1
    The user requested (constraint) zope==4.5.5

Note: I did not add a changelog entry for this internal change.

[mister-roboto]

@mauritsvanrees thanks for creating this Pull Request and helping to improve Plone!

TL;DR: Finish pushing changes, pass all other checks, then paste a comment:

@jenkins-plone-org please run jobs

To ensure that these changes do not break other parts of Plone, the Plone test suite matrix needs to pass, but it takes 30-60 min. Other CI checks are usually much faster and the Plone Jenkins resources are limited, so when done pushing changes and all other checks pass either start all Jenkins PR jobs yourself, or simply add the comment above in this PR to start all the jobs automatically.

Happy hacking!

[mauritsvanrees]

@jenkins-plone-org please run jobs