Argh, make another markup fix

Doc/whatsnew/whatsnew25.tex

@@ -1821,7 +1821,7 @@ Changes to Python's build process and to the C API include:
 \item The largest change to the C API came from \pep{353},
 which modifies the interpreter to use a \ctype{Py_ssize_t} type
 definition instead of \ctype{int}.  See the earlier
-section~ref{section-353} for a discussion of this change.
+section~\ref{section-353} for a discussion of this change.
 
 \item The design of the bytecode compiler has changed a great deal, to
 no longer generate bytecode by traversing the parse tree.  Instead