fix: pin idna<3 version becasue of version conflict between urlextract & requests

[karlicoss]

can be resolved after psf/requests#5710 is fixed

[seanbreckenridge]

@karlicoss since psf/requests#5868 has been merged, I think the pin can be removed?

Causes an error for me because of version conflicts with other stuff I have installed:

$ promnesia index
Traceback (most recent call last):
  File "/home/sean/.local/lib/python3.9/site-packages/pkg_resources/__init__.py", line 568, in _build_master
    ws.require(__requires__)
  File "/home/sean/.local/lib/python3.9/site-packages/pkg_resources/__init__.py", line 886, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/home/sean/.local/lib/python3.9/site-packages/pkg_resources/__init__.py", line 777, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)
pkg_resources.ContextualVersionConflict: (idna 3.3 (/home/sean/.local/lib/python3.9/site-packages), Requirement.parse('idna<3'), {'promnesia'})

[karlicoss]

yep, good catch, looks like not needed anymore