[execution.syn] Add missing \exposid (cplusplus#7181)

Author: hewillk

source/exec.tex

@@ -730,10 +730,10 @@
 if \tcode{value_types_of_t<Sndr, Env, tuple, variant>} is
 \tcode{variant<tuple<>>} or \tcode{vari\-ant<>},
 \item
-Otherwise, \tcode{value_types_of_t<Sndr, Env, decayed-tuple, type_identity_t>}
+Otherwise, \tcode{value_types_of_t<Sndr, Env, \exposid{decayed-tuple}, type_identity_t>}
 if that type is well-formed,
 \item
-Otherwise, \tcode{single-sender-value-type<Sndr, Env>} is ill-formed.
+Otherwise, \tcode{\exposid{single-sender-value-type}<Sndr, Env>} is ill-formed.
 \end{itemize}
 
 \pnum