[c.mb.wcs] Update to refer to C23 7.30.2, 7.31.6.4, 7.31.6.5

... due to new sections added after WG14 N3220

Author: frederick-vs-ja

source/text.tex

@@ -13368,4 +13368,4 @@
 with an \tcode{mbstate_t*} argument that is a null pointer value.
 \end{itemdescr}
 
-\xrefc{7.30.1, 7.31.6.3, 7.31.6.4}
+\xrefc{7.30.2, 7.31.6.4, 7.31.6.5}