A typo in VTKQtCMakeLists file

Dear VTK Developers,

There is a mistake in line 64 https://gitlab.kitware.com/vtk/vtk-examples/-/blob/master/src/Admin/VTKQtCMakeLists#L64

${UISrcs} should be changed to ${UI_FILES}, which prevents Qt from identifying .ui file in qt-creator. Nonetheless, not changing it doesn't cause any issues, just some compile errors in qt-creator.

Regards