Pip now ships with a full resolver, code likely needs updating based on outdated comment

I saw this comment:
https://github.com/dependabot/dependabot-core/blob/9c090f6fe573aa3b6b05d20920c7c48f5f00403f/python/lib/dependabot/python/update_checker.rb#L109-L115

However, `pip` now ships with a real resolver: https://pyfound.blogspot.com/2020/11/pip-20-3-new-resolver.html

I'm not familiar enough with the underlying Dependabot code to know if there's really a potential problem lurking, or if it's just a stale comment.

At a minimum, the comment needs updating at some point.