Fixes this error:

In file included from /builddir/build/BUILD/MuseScore-4.2.1/redhat-linux-build/src/importexport/musicxml/CMakeFiles/iex_musicxml.dir/Unity/unity_1_cxx.cxx:4:
/builddir/build/BUILD/MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.cpp: In function ‘QString mu::engraving::checkAtEndElement(const QXmlStreamReader&, const QString&)’:
/builddir/build/BUILD/MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.cpp:343:9: error: invalid use of incomplete type ‘const class QXmlStreamReader’
  343 |     if (e.isEndElement() && e.name() == expName) {
      |         ^
In file included from /usr/include/qt5/QtXml/QDomElement:1,
                 from /builddir/build/BUILD/MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.h:26,
                 from /builddir/build/BUILD/MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.cpp:33:
/usr/include/qt5/QtXml/qdom.h:94:7: note: forward declaration of ‘class QXmlStreamReader’
   94 | class QXmlStreamReader;
      |       ^~~~~~~~~~~~~~~~
/builddir/build/BUILD/MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.cpp:343:29: error: invalid use of incomplete type ‘const class QXmlStreamReader’
  343 |     if (e.isEndElement() && e.name() == expName) {
      |                             ^
/usr/include/qt5/QtXml/qdom.h:94:7: note: forward declaration of ‘class QXmlStreamReader’
   94 | class QXmlStreamReader;
      |       ^~~~~~~~~~~~~~~~
/builddir/build/BUILD/MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.cpp:349:24: error: invalid use of incomplete type ‘const class QXmlStreamReader’
  349 |                   .arg(e.tokenString())
      |                        ^
/usr/include/qt5/QtXml/qdom.h:94:7: note: forward declaration of ‘class QXmlStreamReader’
   94 | class QXmlStreamReader;
      |       ^~~~~~~~~~~~~~~~
/builddir/build/BUILD/MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.cpp:350:24: error: invalid use of incomplete type ‘const class QXmlStreamReader’
  350 |                   .arg(e.name().toString());
      |                        ^
/usr/include/qt5/QtXml/qdom.h:94:7: note: forward declaration of ‘class QXmlStreamReader’
   94 | class QXmlStreamReader;
      |       ^~~~~~~~~~~~~~~~

--- MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.cpp.orig	2024-01-23 02:35:14.000000000 -0700
+++ MuseScore-4.2.1/src/importexport/musicxml/internal/musicxml/musicxmlsupport.cpp	2024-02-04 20:17:07.403165048 -0700
@@ -24,6 +24,8 @@
  MusicXML support.
  */
 
+#include <QXmlStreamReader>
+
 #include "translation.h"
 #include "engraving/dom/accidental.h"
 #include "engraving/dom/articulation.h"