[cstdio.syn] Update to refer to C23 7.23.3, 7.23

Author: frederick-vs-ja

source/iostreams.tex

@@ -18990,15 +18990,15 @@
 The return from each function call
 that delivers data
 to the host environment
-to be written to a file (\xrefc{7.21.3})
+to be written to a file (\xrefc{7.23.3})
 is an observable checkpoint\iref{intro.abstract}.
 
 \pnum
 Calls to the function \tcode{tmpnam} with an argument that is a null pointer value may
 introduce a data race\iref{res.on.data.races} with other calls to \tcode{tmpnam} with
 an argument that is a null pointer value.
 
-\xrefc{7.21}
+\xrefc{7.23}
 
 \rSec2[cinttypes.syn]{Header \tcode{<cinttypes>} synopsis}