PyJobTransforms: use default asetup for sub-steps running in different release

When running a sub-step (e.g. RDOtoRDOTrigger) in a different release, use the asetup alias (defined by setupATLAS) to setup the release instead of the $AtlasSetup from the user environment. The latter may point to the beta version on afs that is not accessible from within the container.

For my environment, this changes the setup.RDOtoRDOTrigger.sh file from

source /afs/cern.ch/atlas/software/dist/beta/AtlasSetup/scripts/asetup.sh Athena,21.0,latest

to

asetup Athena,21.0,latest

cc @okuprash

Follow-up fix: !71430 (merged)