Fix doc warnings in What's New in 3.11 (GH-92215)

Author: Fidget-Spinner

Doc/whatsnew/3.11.rst

@@ -1396,7 +1396,7 @@ C API Changes
   fields of the result from the exception instance (the ``value`` field).
   (Contributed by Irit Katriel in :issue:`45711`.)
 
-* :c:struct:`_frozen` has a new ``is_package`` field to indicate whether
+* :c:type:`_frozen` has a new ``is_package`` field to indicate whether
   or not the frozen module is a package.  Previously, a negative value
   in the ``size`` field was the indicator.  Now only non-negative values
   be used for ``size``.