[c.math.abs] Update to refer to C23 7.12.8.3, 7.24.7.1

... partially due to new sections added after WG14 N3220

Author: frederick-vs-ja

source/numerics.tex

@@ -9895,7 +9895,7 @@
 The absolute value of \tcode{x}.
 \end{itemdescr}
 
-\xrefc{7.12.7.2, 7.22.6.1}
+\xrefc{7.12.8.3, 7.24.7.1}
 
 \rSec2[c.math.hypot3]{Three-dimensional hypotenuse}