Update mc.Sh_Example3.py
We need this patch because of the introduction of the Sherpa 3.x in this MR atlas/athena!64295 (merged)
Tag @ewelina @fsiegert @cgutscho
Edit: yes, I know that probably the current control card will not work with the Sherpa v3, but that is the next issue to be solved.
Edited by Andrii Verbytskyi