[mdspan.sub.extents] Fix typo

Author: Andreas-Krug

source/containers.tex

@@ -25893,7 +25893,7 @@
 
 \begin{itemdescr}
 \pnum
-Let \tcode{slices} be the pack intoduced by the following declaration:
+Let \tcode{slices} be the pack introduced by the following declaration:
 \begin{codeblock}
 auto [...slices] = submdspan_canonicalize_slices(src, raw_slices...);
 \end{codeblock}