As per PEP-0394[1], there is no real concensus over what binary names
Python has, specifically 'python' could be Python 3, Python 2, or not
exist.
However, everyone has a python3 interpreter and the scripts are all
written for Python 3. Unify the shebangs so that the ~50% of shebangs
that use python now use python3.
[1] https://peps.python.org/pep-0394/