fixed #13853 - updated Qt to 6.9.0

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D:\a\cppcheck\Qt\6.9.0\msvc2022_64\include\QtCharts\qxyseries.h(132,10): error C2143: syntax error: missing ';' before '<' [D:\a\cppcheck\cppcheck\build\gui\cppcheck-gui.vcxproj]
  (compiling source file '../../gui/statsdialog.cpp')

This is caused by the header using the deprecated QPair which we disabled.

Update: I filed https://bugreports.qt.io/browse/QTBUG-135637 about it.

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/home/runner/work/cppcheck/cppcheck/cmake.output/gui/test/resultstree/__/__/moc_projectfile.cpp:40:5: error: 'QtMocHelpers::StringRefStorage' may not intend to support class template argument deduction [clang-diagnostic-ctad-maybe-unsupported]
   40 |     QtMocHelpers::StringRefStorage qt_stringData {
      |     ^
/home/runner/work/cppcheck/Qt/6.9.0/gcc_64/include/QtCore/qtmochelpers.h:57:39: note: add a deduction guide to suppress this warning
   57 | template <typename... Strings> struct StringRefStorage
      |                                       ^

/home/runner/work/cppcheck/cppcheck/cmake.output/gui/test/resultstree/__/__/moc_projectfile.cpp:44:5: error: 'QtMocHelpers::UintData' may not intend to support class template argument deduction [clang-diagnostic-ctad-maybe-unsupported]
   44 |     QtMocHelpers::UintData qt_methods {
      |     ^
/home/runner/work/cppcheck/Qt/6.9.0/gcc_64/include/QtCore/qtmochelpers.h:211:37: note: add a deduction guide to suppress this warning
  211 | template <typename... Block> struct UintData
      |                                     ^

I filed https://bugreports.qt.io/browse/QTBUG-135638 about this.

Update: This causes a build failure with Visual Studio 2019.

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Qt 6.8.x already removed support for VS2019: https://doc.qt.io/qt-6.8/windows.html. So we should/need to remove that combination from the CI.

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Successful installer build with changes applied: https://github.com/danmar/cppcheck/actions/runs/15045760579.

I gave it a short spin and the GUI seems to work fine.