[django-filter] Broaden OrderingFilter fields parameter type

[smelnikov]

The type annotation for the fields parameter in OrderingFilter was incomplete.

According to the documentation:
https://django-filter.readthedocs.io/en/stable/ref/filters.html#django_filters.filters.OrderingFilter

fields is a mapping of {model field name: parameter name}. The parameter names are exposed in the choices and mask/alias the field names used in the order_by() call. Similar to field choices, fields accepts the ‘list of two-tuples’ syntax that retains order. fields may also just be an iterable of strings. In this case, the field names simply double as the exposed parameter names.

https://github.com/carltongibson/django-filter/blob/17ec565554bea4119ad74d2ffccdfb9740d9845b/django_filters/filters.py#L799-L800

Notes

The incorrect type has been present since commit 893b9a7, affecting versions starting from types-django-filter==25.1.0.20250815.

If possible, guidance on how to submit a backport PR for an older stub version would be appreciated.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[srittau]

Thanks, unfortunately, typeshed doesn't support backporting changes to older stub versions.