Fix some qt6 compile error

src/app/kompareurldialog.cpp

@@ -98,7 +98,7 @@ void KompareURLDialog::accept()
         if (QFileInfo(m_diffPage->m_excludeFileURLComboBox->currentText()).isDir())
         {
             qCDebug(KOMPARESHELL) << "Don't enter directory names where filenames are expected..." ;
-            KMessageBox::sorry(this, i18n("File used for excluding files cannot be found, please specify another file."));
+            KMessageBox::error(this, i18n("File used for excluding files cannot be found, please specify another file."));
             reject();
             return;
         }

src/app/main.cpp

@@ -41,8 +41,9 @@
  */
 int main(int argc, char* argv[])
 {
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QApplication::setAttribute(Qt::AA_UseHighDpiPixmaps, true);
-
+#endif
     QApplication app(argc, argv);
     KLocalizedString::setApplicationDomain("kompare");
 

src/dialogpages/diffpage.h

@@ -10,13 +10,13 @@
 #define DIFFPAGE_H
 
 #include <QFrame>
+#include <QStringList>
 
 #include "dialogpages_export.h"
 
 class QCheckBox;
 class QDialog;
 class QSpinBox;
-class QStringList;
 class QButtonGroup;
 class QGroupBox;
 class QTabWidget;