calendar: fix iteration

Fixes #15826

Author: hauntsaninja

stdlib/@tests/stubtest_allowlists/common.txt

@@ -238,6 +238,8 @@ _?ctypes.Union.__setattr__  # doesn't exist, but makes things easy if we pretend
 # Iterable classes that don't define __iter__ at runtime (usually iterable via __getitem__)
 # These would ideally be special-cased by type checkers; see https://github.com/python/mypy/issues/2220
 _?ctypes.Array.__iter__
+calendar._localized_day.__iter__
+calendar._localized_month.__iter__
 
 dataclasses.KW_ONLY  # white lies around defaults
 

stdlib/calendar.pyi

@@ -2,7 +2,7 @@ import datetime
 import enum
 import sys
 from _typeshed import Unused
-from collections.abc import Iterable
+from collections.abc import Iterable, Iterator
 from time import struct_time
 from typing import ClassVar, Final, TypeAlias, overload
 
@@ -170,6 +170,7 @@ class _localized_month:
     def __getitem__(self, i: slice) -> list[str]: ...
 
     def __len__(self) -> int: ...
+    def __iter__(self) -> Iterator[str]: ...
 
 class _localized_day:
     format: str
@@ -181,6 +182,7 @@ class _localized_day:
     def __getitem__(self, i: slice) -> list[str]: ...
 
     def __len__(self) -> int: ...
+    def __iter__(self) -> Iterator[str]: ...
 
 day_name: _localized_day
 day_abbr: _localized_day