[exec.cmplsig] Add 'value_types_of_t' to index (#8326)

Author: jensmaurer

source/exec.tex

@@ -6143,7 +6143,7 @@
            template<class...> class Tuple = @\exposid{decayed-tuple}@,
            template<class...> class Variant = @\exposid{variant-or-empty}@>
       requires @\libconcept{sender_in}@<Sndr, Env>
-    using value_types_of_t =
+    using @\libglobal{value_types_of_t}@ =
       @\exposid{gather-signatures}@<set_value_t, completion_signatures_of_t<Sndr, Env>, Tuple, Variant>;
 
   template<class Sndr, class Env = env<>,