gui: disable font antialiasing for QR image address

More info available here: https://doc.qt.io/qt-5/qfont.html#StyleStrategy-enum

src/qt/qrimagewidget.cpp

@@ -71,6 +71,7 @@ bool QRImageWidget::setQR(const QString& data, const QString& text)
 
     if (!text.isEmpty()) {
         QFont font = GUIUtil::fixedPitchFont();
+        font.setStyleStrategy(QFont::NoAntialias);
         QRect paddedRect = qrAddrImage.rect();
 
         // calculate ideal font size