apply black and isort (#4287)

* apply black and isort

* move some type ignores

stdlib/3/posix.pyi

@@ -3,9 +3,8 @@
 # NOTE: These are incomplete!
 
 import sys
-from typing import List, NamedTuple, Optional, overload
-
 from os import stat_result as stat_result
+from typing import List, NamedTuple, Optional, overload
 
 if sys.version_info >= (3, 6):
     from builtins import _PathLike  # See comment in builtins
@@ -117,6 +116,7 @@ if sys.version_info >= (3, 6):
     def listdir(path: int) -> List[str]: ...
     @overload
     def listdir(path: _PathLike[str]) -> List[str]: ...
+
 else:
     @overload
     def listdir(path: Optional[str] = ...) -> List[str]: ...