[intro.abstract] Update to refer to C23 7.23.3

Author: frederick-vs-ja

source/intro.tex

@@ -1019,7 +1019,7 @@
 Accesses through volatile glvalues are evaluated strictly according to the
 rules of the abstract machine.
 \item
-Data is delivered to the host environment to be written into files (\xrefc{7.21.3}).
+Data is delivered to the host environment to be written into files (\xrefc{7.23.3}).
 
 \begin{note}
 Delivering such data