Fix MC21 Zmumu input for TrigInDetValidation ART
Fix for two ART tests.
The mu_zmumu_pu40
and mulrt_zmumu_pu40
TrigInDetValidation ART tests have stopped working because their MC15 input datasets no longer exist. They were presumably removed in a recent cleanup. This MR updates the files to use MC21 inputs. The ttbar tests have already been updated; others will follow.