[meta.syn] Fix typo "type_underlying_type" => "underlying_type"

This was an error in P2996R13.

Author: tkoeppe

source/meta.tex

@@ -3266,7 +3266,7 @@
     consteval info common_type(R&& type_args);
   template<@\libconcept{reflection_range}@ R = initializer_list<info>>
     consteval info common_reference(R&& type_args);
-  consteval info type_underlying_type(info type);
+  consteval info underlying_type(info type);
   template<@\libconcept{reflection_range}@ R = initializer_list<info>>
     consteval info invoke_result(info type, R&& type_args);
   consteval info unwrap_reference(info type);