cmssw: /usr/bin/env: python3: No such file or directory

we stil get error like /usr/bin/env: python3: No such file or directory on top of CMSSW_12_0_X_2021-05-04-2300

To reproduce:

1. script that try to run https://gitlab.cern.ch/cms-nanoAOD/nanoAOD-integration/-/blob/master/scripts/setup_reference.sh https://gitlab.cern.ch/cms-nanoAOD/nanoAOD-integration/-/blob/master/scripts/find_latest_IB.sh

2. Full Log with error https://gitlab.cern.ch/cms-nanoAOD/nanoAOD-integration/-/jobs/13650096

@gouskos @silviodonato @smuzaffar