'Module has no attribute "xxx"' when mixing `py_binary` deps and `__init__` reexports

Thanks for the great work on this project! We've adopted it throughout parts of our monorepo and we really like it.

While trying to expand our usage of `rules_mypy`, I've run into an issue which I believe is a bug. I was able to produce a minimal example, which seems to have something to do with `__init__.py` files that depend on `py_binary` targets (rather than `py_library`).

For clarity, `rules_python` allows depending on `py_binary` targets as if they were `py_library`s. There isn't really any difference, except the presence of a `if __name__ == "__main__":` block which is ignored. We have several library files with small main sections at the bottom for ad-hoc debugging.

# MRE

`example/BUILD.bazel`
```
py_binary(
name = "main",
srcs = ["main.py"],
deps = ["//example/foo:__init__"],
)
```

`example/main.py`
```python
import example.foo as foo

if __name__ == "__main__":
print(foo.do_something())
```

`example/foo/BUILD.bazel`
```
py_library(
name = "__init__",
srcs = ["__init__.py"],
deps = [":a"],
)

py_binary(
name = "a",
srcs = ["a.py"],
)
```

`example/foo/__init__.py`
```python
from example.foo.a import do_something

__all__ = ["do_something"]
```

`example/foo/a.py`
```python
def do_something():
return "hello"

if __name__ == "__main__":
print(do_something())
```

## Result

When I run `bazel build //example/...` I see the following error:

```bash
example/main.py:4: error: Module has no attribute "do_something" [attr-defined]
```

Removing the `if __name__ == "__main__"` from `a.py` and switching to a `py_library` target causes this example to succeed. Outside of bazel, mypy does not complain about either case.

Start with the minimal reproduction in example/BUILD.bazel, example/main.py, example/foo/BUILD.bazel, example/foo/__init__.py, and example/foo/a.py. Run bazel build //example/... and compare the py_binary dependency case with the py_library case; done means the reproduced import no longer reports the missing do_something attribute.

Written by the indexing model from the issue text.