Please branch and build python-nose in epel9. If you do not wish to maintain python-nose in epel9, or do not think you will be able to do this in a timely manner, the EPEL Packagers SIG would be happy to be a co-maintainer of the package; please add the epel-packagers-sig group through https://src.fedoraproject.org/rpms/python-nose/addgroup and grant it commit access, or collaborator access on epel* branches. I would also be happy to be a co-maintainer (FAS: jonathanspw). I can be the primary contact for EPEL (FAS: jonathanspw).
The python-nose package is deprecated[1] because it is unmaintained upstream. It should not be branched into EPEL9. The linked wiki page has suggestions for working around a nose dependency. [1] https://fedoraproject.org/wiki/Changes/DeprecateNose *** This bug has been marked as a duplicate of bug 2041068 ***
Note that python-hglib has a custom nose plugin, so using nose2 or pytest might be non-trivial. Possible, but would require patching, since python-hglib itself is a long-dead project.