Fix Qt6 building (#4393)

src/widgets/settingspages/AboutPage.cpp

@@ -8,6 +8,7 @@
 #include "widgets/BasePopup.hpp"
 #include "widgets/helper/SignalLabel.hpp"
 
+#include <QFile>
 #include <QFormLayout>
 #include <QGroupBox>
 #include <QLabel>
@@ -144,7 +145,11 @@ AboutPage::AboutPage()
             contributorsFile.open(QFile::ReadOnly);
 
             QTextStream stream(&contributorsFile);
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+            // Default encoding of QTextStream is already UTF-8
+#else
             stream.setCodec("UTF-8");
+#endif
 
             QString line;