[exec.snd.expos] Mark exposition-only identifier with \exposid (#7531)

Author: ericniebler

source/exec.tex

@@ -1636,7 +1636,7 @@
 
     using @\exposid{tag-t}@ = tag_of_t<Sndr>;                               // \expos
     using @\exposid{state-t}@ = @\exposid{state-type}@<Sndr, Rcvr>;                     // \expos
-    static constexpr const auto& @\exposid{complete}@ = @\exposid{impls-for}@<tag-t>::@\exposid{complete}@;   // \expos
+    static constexpr const auto& @\exposid{complete}@ = @\exposid{impls-for}@<@\exposid{tag-t}@>::@\exposid{complete}@;   // \expos
 
     template<class... Args>
       requires @\exposconcept{callable}@<decltype(@\exposid{complete}@), Index, @\exposid{state-t}@&, Rcvr&, set_value_t, Args...>