[meta.reflection.result] Fix "variable" => "template"

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

Author: tkoeppe

source/meta.tex

@@ -6114,7 +6114,7 @@
 \throws
 \tcode{meta::exception} unless
 the \grammarterm{template-id} \tcode{TCls<$V$>} would be valid
-given the invented variable
+given the invented template
 \begin{codeblock}
 template<T P> struct TCls;
 \end{codeblock}