__init__.pyi: Add __getitem__() to stat_result()

Fixes python#2751

Author: utkarsh2102

stdlib/3/os/__init__.pyi

@@ -216,7 +216,7 @@ class stat_result:
     st_mtime_ns: int  # time of most recent content modification in nanoseconds
     st_ctime_ns: int  # platform dependent (time of most recent metadata change on Unix, or the time of creation on Windows) in nanoseconds
 
-    def __getitem__(self, key: AnyStr) -> AnyStr: ...
+    def __getitem__(self, i: int) -> int: ...
 
     # not documented
     def __init__(self, tuple: Tuple[int, ...]) -> None: ...