[meta.reflection.queries] Add missing comma in "function, type".

This seems to have been a mistake during application of P2996R13.

Author: tkoeppe

source/meta.tex

@@ -4318,7 +4318,12 @@
 \begin{itemdescr}
 \pnum
 \returns
-\tcode{true} if \tcode{r} represents a variable, function type, template, or namespace
+\tcode{true} if \tcode{r} represents a
+variable,
+function,
+type,
+template, or
+namespace
 whose name has
 internal linkage,
 module linkage,