[dcl.fct.default] Add \tcode for a

Author: Andreas-Krug

source/declarations.tex

@@ -4530,7 +4530,7 @@
   int mem1(int i = a);                      // error: non-static member \tcode{a} used as default argument
   int mem2(int i = b);                      // OK, use \tcode{X::b}
   consteval void mem3(std::meta::info r = ^^a) {}   // OK
-  int mem4(int i = [:^^a:]);                // error: non-static member a designated in default argument
+  int mem4(int i = [:^^a:]);                // error: non-static member \tcode{a} designated in default argument
   static int b;
 };
 \end{codeblock}