fix quotation marks in 5.2.25

Author: UlrikBuchholtz

actions.tex

@@ -552,7 +552,7 @@ \subsection{Actions in a type}
   \[
     X : \BG \to A.
   \]
-  The particular "object of type $A$ being acted on" is $X(\sh_G):A$,
+  The particular ``object of type $A$ being acted on'' is $X(\sh_G):A$,
   the \emph{underlying object}.%
   \index{action!of a group in a type}