[intro.races] Fix typo

Author: lprv

source/basic.tex

@@ -6806,7 +6806,7 @@
 \item $A$ happens before $B$ and
 \item there is no other
 \indextext{side effects}%
-side effect $X$ to $M$ such that $A$
+side effect $X$ on $M$ such that $A$
 happens before $X$ and $X$ happens before $B$.
 \end{itemize}