CKAN version

2.9.5

Describe the bug

Obsolete requirements:

• pytz is pinned to 2016, https://github.com/ckan/ckan/blob/2.9/requirements.in#L23
• Zope.interface is pinned to a version from 2016, prior to python 3.6 support. https://github.com/ckan/ckan/blob/2.9/requirements.in#L38 (ref: https://pypi.org/project/zope.interface/)

Specifically, (at least on python 3) the zope.interface pin is the one that's preventing us from using modern setuptools and requiring a pin. (at least, until one installs ckanext-dcat, which is limited to setuptools<58.0 due to rdflib-jsonld)

Proposed fix

Unpin pytz. Update zope.interface to <5.0