Revert bad formatting inside listing

Co-authored-by: Hans Olsson <HansOlsson@users.noreply.github.com>

chapters/classes.tex

@@ -390,7 +390,7 @@ \subsection{Component Variability Prefixes discrete, parameter, constant}\label{
 
 \begin{lstlisting}[language=modelica]
 model PiecewiseConstantReals
-  discrete Real xd1 "Must be assigned in a \lstinline!when!-clause, discrete-time";
+  discrete Real xd1 "Must be assigned in a when-clause, discrete-time";
   Real xd2 "Assigned in a \lstinline!when!-clause (below) and thus discrete-time";
   Real xc3 "Not discrete-time, but piecewise constant";
   Real x4 "Piecewise constant, but changes between events";