[mdspan.layout.leftpad.overview] Add missing \tcode (#6958)

Author: hewillk

source/containers.tex

@@ -21061,7 +21061,7 @@
 \item
 the empty parameter pack, if \exposid{rank_} equals zero;
 \item
-\tcode otherwise, {0zu}, if \exposid{rank_} equals one;
+\tcode otherwise, \tcode{0zu}, if \exposid{rank_} equals one;
 \item
 otherwise, the parameter pack \tcode{0zu}, \tcode{1zu}, \ldots, \tcode{\exposid{rank_}- 1}.
 \end{itemize}