[Python-Dev] Travis CI for backports not working.

Travis passed https://github.com/python/cpython/pull/17366 but a half hour later twice failed https://github.com/python/cpython/pull/17370 https://github.com/python/cpython/pull/17371 saying pyenv: python3.8: command not found pyenv: version `3.7.1' not installed -- Terry Jan Reedy