[intro.races] p13 - add missing serial comma between items

source/basic.tex

@@ -6242,7 +6242,7 @@
 with respect to a value computation $B$ of $M$ satisfies the
 conditions:
 \begin{itemize}
-\item $A$ happens before $B$ and
+\item $A$ happens before $B$, and
 \item there is no other
 \indextext{side effects}%
 side effect $X$ to $M$ such that $A$