clang-tidy: fix `modernize-use-override` lints

Charts/Core/vtkChartBox.h

Charts/Core/vtkPlotArea.h

Charts/Core/vtkPlotBar.h

Charts/Core/vtkPlotFunctionalBag.h

Charts/Core/vtkPlotPoints.h

Charts/Core/vtkPlotStacked.h

Common/Core/SMP/OpenMP/vtkSMPThreadLocalImpl.h

Common/Core/SMP/STDThread/vtkSMPThreadLocalImpl.h

Common/Core/SMP/Sequential/vtkSMPThreadLocalImpl.h

Common/Core/SMP/TBB/vtkSMPThreadLocalImpl.h

Filters/OpenTURNS/vtkOTScatterPlotMatrix.h

Filters/ParallelFlowPaths/vtkPParticleTracerBase.h

Filters/Sources/vtkHandleSource.h

GUISupport/QtQuick/qml/QQmlVTKPlugin.h

IO/ADIOS2/VTX/schema/vtk/VTXvtkBase.h

IO/ADIOS2/VTX/schema/vtk/VTXvtkVTI.h

IO/ADIOS2/VTX/schema/vtk/VTXvtkVTU.h

IO/ADIOS2/vtkADIOS2CoreImageReader.h

IO/ADIOS2/vtkADIOS2VTXReader.h

IO/Core/vtkResourceStream.h