Fixes these errors:

In file included from /builddir/build/BUILD/MuseScore-4.2.1/redhat-linux-build/src/learn/learn_autogen/mocs_compilation.cpp:2,
                 from /builddir/build/BUILD/MuseScore-4.2.1/redhat-linux-build/src/learn/CMakeFiles/learn.dir/Unity/unity_0_cxx.cxx:4:
/builddir/build/BUILD/MuseScore-4.2.1/redhat-linux-build/src/learn/learn_autogen/OTUN7GXZT4/moc_learnpagemodel.cpp: In static member function ‘static void mu::learn::LearnPageModel::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)’:
/builddir/build/BUILD/MuseScore-4.2.1/redhat-linux-build/src/learn/learn_autogen/OTUN7GXZT4/moc_learnpagemodel.cpp:120:31: error: variable ‘QVariantMap _r’ has initializer but incomplete type
  120 |         case 6: { QVariantMap _r = _t->classesAuthor();
      |                               ^~
/builddir/build/BUILD/MuseScore-4.2.1/redhat-linux-build/src/learn/learn_autogen/OTUN7GXZT4/moc_learnpagemodel.cpp:120:53: error: invalid use of incomplete type ‘QVariantMap’ {aka ‘class QMap<QString, QVariant>’}
  120 |         case 6: { QVariantMap _r = _t->classesAuthor();
      |                                    ~~~~~~~~~~~~~~~~~^~
In file included from /usr/include/qt5/QtCore/qglobal.h:1303,
                 from /usr/include/qt5/QtCore/qnamespace.h:43,
                 from /usr/include/qt5/QtCore/qobjectdefs.h:48,
                 from /usr/include/qt5/QtCore/qobject.h:46,
                 from /usr/include/qt5/QtCore/QObject:1,
                 from /builddir/build/BUILD/MuseScore-4.2.1/redhat-linux-build/src/learn/learn_autogen/OTUN7GXZT4/../../../../../src/learn/view/learnpagemodel.h:25,
                 from /builddir/build/BUILD/MuseScore-4.2.1/redhat-linux-build/src/learn/learn_autogen/OTUN7GXZT4/moc_learnpagemodel.cpp:10:
/usr/include/qt5/QtCore/qtypeinfo.h:240:1: note: declaration of ‘QVariantMap’ {aka ‘class QMap<QString, QVariant>’}
  240 | Q_DECLARE_MOVABLE_CONTAINER(QMap);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~

--- MuseScore-4.2.1/src/learn/view/learnpagemodel.h.orig	2024-01-23 02:35:14.000000000 -0700
+++ MuseScore-4.2.1/src/learn/view/learnpagemodel.h	2024-02-05 06:43:36.113753705 -0700
@@ -23,6 +23,8 @@
 #define MU_LEARN_LEARNPAGEMODEL_H
 
 #include <QObject>
+#include <QMap>
+#include <QVariant>
 
 #include "async/asyncable.h"