Update Geant4 version to 10.6.3.8
Update the Geant4 version to 10.6.3.8
.
This is the same as version 10.6.3.7
plus patches for ATLASSIM-6363 and ATLASSIM-6396.
This Geant4 version has been validated in a private build of Athena,23.0 (ATLPHYSVAL-945)