Add maximum mu value in mu-dependent nTRT cut

This is a follow-up on MR 44251. The mu-dependent nTRT cuts have only been validated up to mu = 80; therefore we stop the evolution of the nTRT cut above mu = 80. In addition, there is some physical limit to nTRT, so at some point there needs to be a ceiling for this threshold.

This max mu value would need to be revisited when a higher mu value is reached.