Add __all__ for modules beginning with 'c' and 'd' (#7303)

stdlib/datetime.pyi

@@ -4,6 +4,9 @@ from time import struct_time
 from typing import ClassVar, NamedTuple, NoReturn, SupportsAbs, TypeVar, overload
 from typing_extensions import Literal, final
 
+if sys.version_info >= (3, 9):
+    __all__ = ("date", "datetime", "time", "timedelta", "timezone", "tzinfo", "MINYEAR", "MAXYEAR")
+
 _D = TypeVar("_D", bound=date)
 
 MINYEAR: Literal[1]