www/py-django32: Deprecate/Set to expire

[kai]

Summary

Django 3.2 will reach its End-of-Life in April 2024.

Set the deprecation note and let it expire to the end of June to give enough time to switch all affected ports over to Django 4.2 which is the next LTS release.

PR: 276319

Test Plan

1. Update as many ports during 2024Q1 but keep them assigned to Django 3.2
2. Once 2024Q2 is branched, switch all those ports to Django 4.2
3. Deprecate the py-dj42* ports as they are superfluous then
4. If everything goes well, Django 3.2 should be ready to be deorbited to the end of June 2024
5. Plan B: Extend the deprecation date if some upstream repositories (e.g. for www/py-horizon) need a bit more time

See also: https://wiki.freebsd.org/Ports/Django/Django42Migration