[range.cartesian.view] Add missing \exposid

Author: tkoeppe

source/ranges.tex

@@ -14410,7 +14410,7 @@
 \effects
 Equivalent to:
 \begin{codeblock}
-@\exposid{iterator}@<is-const> it(@\exposid{tuple-transform}@(
+@\exposid{iterator}@<@\exposid{is-const}@> it(@\exposid{tuple-transform}@(
   [](auto& rng){ return @\exposid{begin-or-first-end}@(rng); }, @\exposid{bases_}@));
 return it;
 \end{codeblock}