Support Django v4.2 and v5.0

[sevdog]

Django 4.2 has been released, just the day before this library released its version 2.0.0 (see #23).

Since it does not have any particular breaking changes which may involves this library it should be easy to support it just by adding the value to tox configurations.

So technically this is just a "add tests for Django 4.2" request.

---

PS: in the meantime I want to highlight that this package is still marked to support Django 1.10, even if it is no more configured in tox

https://github.com/CodeYellowBV/django-relativedelta/blob/a62261c287eb49fe88da96bed87668ec82047ee6/setup.py#L58

PPS: Also, setup metadata does not declare to support Django 2.x nor Python3.8 which are in tox configuration and are currently tested. https://github.com/CodeYellowBV/django-relativedelta/blob/a62261c287eb49fe88da96bed87668ec82047ee6/setup.py#L41-L50

[Mapiarz]

Bump with support for 5.0 ;)