Correct type for db.models.sql.query.Query.join() argument

[mthuurne]

The join argument of db.models.sql.query.Query.join() should be an instance, not a class.

I think the confusion comes from the docstring. In Django 3.2 it reads:

'join' is either a sql.datastructures.BaseTable or Join.

The word "a" is ambiguous here: from the join() implementation it's clear that an instance is required, but looking at only the docstring it could be misinterpreted as requiring a subclass.

Note that in the latest Django code, the docstring reads:

'join' is either a base_table_class or join_class.

This is because new base_table_class and join_class attributes were added to db.models.sql.query.Query. I don't know if it's worth adding type arguments to the Query class for this. Either way, I think it would be better to first correct the annotations to work with the non-customized Query use case.

[sobolevn]

Thanks!