[meta.reflection.result] Fix function parameter name

A misapplication of P2996R13.

Author: tkoeppe

source/meta.tex

@@ -6183,7 +6183,7 @@
 \indexlibraryglobal{reflect_function}%
 \begin{itemdecl}
 template<class T>
-  consteval info reflect_function(T& expr);
+  consteval info reflect_function(T& fn);
 \end{itemdecl}
 
 \begin{itemdescr}
@@ -6198,7 +6198,7 @@
 \pnum
 \throws
 \tcode{meta::exception} unless
-\tcode{expr} is suitable for use as a constant template argument
+\tcode{fn} is suitable for use as a constant template argument
 for a constant template parameter of type \tcode{T\&}\iref{temp.arg.nontype}.
 \end{itemdescr}