Add gettext.c2py (#13078)

Add a stub for gettext.c2py

Author: tomasr8

stdlib/gettext.pyi

@@ -167,3 +167,5 @@ if sys.version_info < (3, 11):
     def bind_textdomain_codeset(domain: str, codeset: str | None = None) -> str: ...
 
 Catalog = translation
+
+def c2py(plural: str) -> Callable[[int], int]: ...