Add barcode attribute in Epos_i for HepMC3
HepMC3 requires the barcode attribute to be set, which was previously missing and causing PMG validation to fail for EPOS samples (and in particular, failing since truth particles are written out in these samples, and subsequently rely on xAODTruthCnvAlg.cxx
which throws an error if the barcodes are missing).
Edited by ATLAS Robot