[exec.just,exec.then] Use \exposconcept for movable-value (#7187)

Author: hewillk

source/exec.tex

@@ -2573,7 +2573,7 @@
 The expression \tcode{\exposid{just-cpo}(ts...)} is ill-formed if
 \begin{itemize}
 \item
-\tcode{(\exposid{movable-value}<Ts> \&\&...)} is \tcode{false}, or
+\tcode{(\exposconcept{movable-value}<Ts> \&\&...)} is \tcode{false}, or
 \item
 \exposid{just-cpo} is \tcode{just_error} and
 \tcode{sizeof...(ts) == 1} is \tcode{false}, or
@@ -3308,7 +3308,7 @@
 \tcode{then}, \tcode{upon_error}, or \tcode{upon_stopped}.
 For subexpressions \tcode{sndr} and \tcode{f},
 if \tcode{decltype((sndr))} does not satisfy \libconcept{sender}, or
-\tcode{decltype((f))} does not satisfy \exposid{movable-value},
+\tcode{decltype((f))} does not satisfy \exposconcept{movable-value},
 \tcode{\exposid{then-cpo}(\linebreak sndr, f) }is ill-formed.
 
 \pnum