OSError.errno can be None (#12910)

stdlib/builtins.pyi

@@ -1916,7 +1916,7 @@ class StopIteration(Exception):
     value: Any
 
 class OSError(Exception):
-    errno: int
+    errno: int | None
     strerror: str
     # filename, filename2 are actually str | bytes | None
     filename: Any