fields type in bulk_update

[jerch]

Bug report

What's wrong

The fields argument in bulk_update is typed as Sequence[str]:

django-stubs/django-stubs/db/models/query.pyi

Line 62 in a9e41a8

def bulk_update(self, objs: Iterable[_T], fields: Sequence[str], batch_size: Optional[int] = ...) -> int: ...

This prevents using Set[str], as it is not a subtype of Sequence (thats my actual issue with it).

How is that should be

Looking at the django source bulk_update transforms the fields argument by a list comprehension early, thus any iterable should work here. I suggest to widen the type info to Iterable[str].

[sobolevn]

PR is welcome.