After the addition of Python 3.8 in #3874, the default python3 is
now /usr/local/bin/python3. The nanopb Dockerfile hardcoded a path
of /usr/bin/python3, causing again problems of Python packages being
installed for different version than attempting to run with.
This remaps /usr/bin/python as python3, because grpcio-tools support
for Python 2 has ended. Nanopb generator still uses #!/usr/bin/env python
so it would pick Python 2 by default otherwise.
Anaconda was used in a previous pull request to attempt installing a working
combination of libraries, but it is unnecessary once the version conflict was
fixed.
devtty1er