Add CTYPES_MAX_ARGCOUNT to _ctypes (#8601)

stdlib/_ctypes.pyi

@@ -2,6 +2,9 @@ import sys
 from ctypes import _CArgObject, _PointerLike
 from typing_extensions import TypeAlias
 
+if sys.version_info >= (3, 11):
+    CTYPES_MAX_ARGCOUNT: int
+
 if sys.platform == "win32":
     # Description, Source, HelpFile, HelpContext, scode
     _COMError_Details: TypeAlias = tuple[str | None, str | None, str | None, int | None, int | None]