[format.arg] Fix parameter type for basic_format_arg constructor.

Author: jensmaurer

source/utilities.tex

@@ -21092,7 +21092,7 @@
 \end{itemdescr}
 
 \begin{itemdecl}
-template<class T> explicit basic_format_arg(T* p) noexcept;
+template<class T> explicit basic_format_arg(const T* p) noexcept;
 \end{itemdecl}
 
 \begin{itemdescr}