Fix typo in runIDPVM.py
A recent change in runIDPVM.py introduced a typo which causes:
Traceback (most recent call last):
File "/cvmfs/atlas-nightlies.cern.ch/repo/sw/master_Athena_x86_64-centos7-gcc11-opt/2022-06-28T2101/Athena/23.0.2/InstallArea/x86_64-centos7-gcc11-opt/share/runIDPVM.py", line 53, in <module>
ConfigFlags.PhysVal.IDPVM.truthMinPt = MyArgs.truthMinP
AttributeError: 'Namespace' object has no attribute 'truthMinP'
This MR fixes the small typo.
cc @tstreble