Adding path to the python executable to the environment did the trick:
PYTHON=/usr/bin/python3 ./upgrade_5.1_6.0.sh
All upgrade scripts ran without errors. Now on to the details.
Adding path to the python executable to the environment did the trick:
PYTHON=/usr/bin/python3 ./upgrade_5.1_6.0.sh
All upgrade scripts ran without errors. Now on to the details.