Don't use upper bound pins

Quoting Richard Si

From the post on What's new in pip 25.1 - Dependency groups!, a footnote on improvements to Pip's dependency resolution:

Please don’t add upper bounds unless you know for a fact your codebase is incompatible with the newer versions. Pre-emptive upper-bounds will not help dependency resolution and are generally considered harmful.

Nice to have an authoritative something to link to when trying to make this case to package maintainers.