Doesn't build with QT 6.11.0 on linux

``` # github.com/mappu/miqt/qt6 In file included from gen_qstringconverter.cpp:4: In file included from /usr/include/qt6/QtCore/QStringConverterBase:1: /usr/include/qt6/QtCore/qstringconverter_base_deprecated.h:18:4: warning: "QStringConverterBase is not a public class and including " "<QtCore/QStringConverterBase> is deprecated. The header will disappear" " in Qt 7" [-W#warnings] # github.com/mappu/miqt/qt6 In file included from gen_qstringconverter_base.cpp:2: In file included from /usr/include/qt6/QtCore/QStringConverterBase:1: /usr/include/qt6/QtCore/qstringconverter_base_deprecated.h:18:4: warning: "QStringConverterBase is not a public class and including " "<QtCore/QStringConverterBase> is deprecated. The header will disappear" " in Qt 7" [-W#warnings] # github.com/mappu/miqt/qt6 gen_qvariant.cpp:36:10: fatal error: 'QVariantConstPointer' file not found ``` I had to downgrade to version 6.10 to be able to compile, but that broke parts of my system that needed version 6.11.