[exec.sync.wait] Add \tcode for apply_sender (#7538)

Author: ericniebler

source/exec.tex

@@ -4564,7 +4564,7 @@
 The type \tcode{\exposid{sync-wait-result-type}<Sndr>} is well-formed.
 \item
 \tcode{\libconcept{same_as}<decltype($e$), \exposid{sync-wait-result-type}<Sndr>>}
-is \tcode{true}, where $e$ is the apply_sender expression above.
+is \tcode{true}, where $e$ is the \tcode{apply_sender} expression above.
 \end{itemize}
 
 \pnum