[mdspan.layout.left.cons] Fix typo (cplusplus#7360)

Author: Andreas-Krug

source/containers.tex

@@ -20760,7 +20760,7 @@
 
 \indexlibraryctor{layout_left::mapping}%
 \begin{itemdecl}
-template<class OtherExents>
+template<class OtherExtents>
   constexpr explicit(!is_convertible_v<OtherExtents, extents_type>)
     mapping(const layout_right::mapping<OtherExtents>& other) noexcept;
 \end{itemdecl}