* Allow Collection for 'fields' and 'exclude' of form model helpers (#637)
There are several functions and classes in `django.forms.models` that
take a `fields` or `exclude` argument. Previously, `Sequence` was used
to annotate these, but the code of Django (I checked version 3.2.4)
doesn't require `__getitem__()` to be implemented, so requiring
`Collection` instead is sufficient.
The practical advantage of requiring `Collection` is that a set, such
as the key set of a dictionary, can be passed without first having to
convert it to a list or tuple.
* Pin mypy to below version 0.900
* Remove Callable for 'fields' and 'exclude' of form model helpers
I cannot find any support for callables for these two arguments in
the code or in the documentation.
* Update setup.py
Co-authored-by: Nikita Sobolev <mail@sobolevn.me>
