[mypyc] AssertionError in get_seuqnce_type on `ois.uname`

**Bug Report**

`mypyc` is asserting on a type defined to be an iterable.

**To Reproduce**

`mypyc foo.py`

```python
import os

for component in os.uname():
    print(component.encode())
```

**Expected Behavior**

No assertion :smile: 

**Actual Behavior**

Assertion :cry: 

(Write what happened.)

**Your Environment**

N/A
