Partial compile fix for current Qt dev and/or Qt 6

This does not cover Utils::MapReduceOption with QVector, and code
that's not compiled on my machine.

Change-Id: Ib63923985c52b1bb74e5ec2068a2bb37469ac618
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/help/textbrowserhelpviewer.cpp

@@ -458,9 +458,17 @@ void TextBrowserHelpWidget::resizeEvent(QResizeEvent *e)
     scrollToTextPosition(topTextPosition);
 }
 
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
 void TextBrowserHelpWidget::setSource(const QUrl &name)
+#else
+void TextBrowserHelpWidget::doSetSource(const QUrl &name, QTextDocument::ResourceType type)
+#endif
 {
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     QTextBrowser::setSource(name);
+#else
+    QTextBrowser::doSetSource(name, type);
+#endif
 
     QTextCursor cursor(document());
     while (!cursor.atEnd()) {