[exec.snd.transform] Mark transformed-sndr with \exposid (#7542)

Author: ericniebler

source/exec.tex

@@ -2287,7 +2287,7 @@
 if \exposid{transformed-sndr} and \exposid{sndr}
 have the same type ignoring cv-qualifiers;
 otherwise, it is
-the expression \tcode{transform_sender(dom, transformed-sndr, env...)}.
+the expression \tcode{transform_sender(dom, \exposid{transformed-sndr}, env...)}.
 
 \pnum
 \returns