[basic.fundamental] Add column divider line

Fixes ISO/CS comment (C++23 proof)

source/basic.tex

@@ -5051,7 +5051,7 @@
 the largest value of the corresponding unsigned type.
 \end{example}
 
-\begin{floattable}{Minimum width}{basic.fundamental.width}{ll}
+\begin{floattable}{Minimum width}{basic.fundamental.width}{l|l}
 \topline
 \lhdr{Type} & \rhdr{Minimum width $N$} \\
 \capsep