After #8358 I went looking for other cases of __iter__ returing Iterable. I found two:

1. https://github.com/python/cpython/blob/934b25dcc492dcbca4da9d63d0d71dc940fc0375/Lib/wsgiref/validate.py#L216-L221 which clearly is an Iterator
2. https://github.com/google/python-gflags/blob/4f06c3d0d6cbe9b1fb90ee9fb1c082b3bf9285f6/gflags/flagvalues.py#L666-L667 which is also an Iterator

According to the docs:

object.__iter__(self)
This method is called when an iterator is required for a container. This method should return a new iterator object that can iterate over all the objects in the container. For mappings, it should iterate over the keys of the container.

Maybe this can be added as a new flake8-pyi rule.