[range.iota.sentinel] Add missing \exposid (#5797)

Author: hewillk

source/ranges.tex

@@ -3354,7 +3354,7 @@
 \end{itemdescr}
 
 \begin{itemdecl}
-friend constexpr iter_difference_t<W> operator-(const @\exposid{iterator}@& x, const sentinel& y)
+friend constexpr iter_difference_t<W> operator-(const @\exposid{iterator}@& x, const @\exposid{sentinel}@& y)
   requires @\libconcept{sized_sentinel_for}@<Bound, W>;
 \end{itemdecl}