Use reference instead of Study::Ptr in functions of tests

[JasonMarechal25]

          Not directly related to that PR but:

Instead of using a shared_ptr, the best thing would be to clarify if this handler should have ownership of the study (I don't think so). If not, we can just pass a reference here. shared_ptr should be used only when shared ownership is actually required. Then we wouldn't need the move :)

Originally posted by @sylvlecl in https://github.com/AntaresSimulatorTeam/Antares_Simulator/pull/1388#discussion_r1276302773