[range.elements.sentinel] Fix incorrect \placeholder (#5526)

Author: hewillk

source/ranges.tex

@@ -8409,8 +8409,8 @@
 \begin{codeblock}
 namespace std::ranges {
   template<@\libconcept{input_range}@ V, size_t N>
-    requires @\libconcept{view}@<V> && @\placeholder{has-tuple-element}@<range_value_t<V>, N> &&
-             @\placeholder{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N> &&
+    requires @\libconcept{view}@<V> && @\exposconcept{has-tuple-element}@<range_value_t<V>, N> &&
+             @\exposconcept{has-tuple-element}@<remove_reference_t<range_reference_t<V>>, N> &&
              @\exposconcept{returnable-element}@<range_reference_t<V>, N>
   template<bool Const>
   class elements_view<V, N>::@\exposid{sentinel}@ {