Fix CI error caused by 9cbac6fe

Include header "rulebookdata.h" instead of class forwarding.
The header is automatically generated by kcmutils_generate_module_data
and includes a namespace

kcmkwin/kwinrules/rulebookmodel.cpp

@@ -6,9 +6,9 @@
 
 #include "rulebookmodel.h"
 
-#include "rulebookdata.h"
 #include "rulebooksettings.h"
 
+
 namespace KWin
 {
 

kcmkwin/kwinrules/rulebookmodel.h

@@ -6,6 +6,7 @@
 
 #pragma once
 
+#include "rulebookdata.h"
 #include <rules.h>
 
 #include <QAbstractListModel>
@@ -14,8 +15,6 @@
 namespace KWin
 {
 
-class RuleBookData;
-
 class RuleBookModel : public QAbstractListModel
 {
     Q_OBJECT