updated herwig 7.2.3
I followed the discussion with top PMG experts, and they mentioned that the differences between Herwig 7.2.1 and 7.2.3 are only for some minbias switches and log file improvements. Physics-wise the two versions are identical.
Since there are already some samples generated with Herwig 7.2.3 (an example here, and got confirmation from algorithms conveners already it's fine to use Herwig 7.2.1 on Herwig 7.2.3 samples), so I'm adding this info.