[iostream.objects.overview] Update to refer to C23 7.23.2

Author: frederick-vs-ja

source/iostreams.tex

@@ -532,7 +532,7 @@
 can result in interleaved characters.
 \end{note}
 
-\xrefc{7.21.2}
+\xrefc{7.23.2}
 
 \rSec2[narrow.stream.objects]{Narrow stream objects}