The docsbuild venv, from https://github.com/python/psf-salt/blob/master/salt/docs/init.sls#L38 runs python 2.7.

It's only used to run sphinx (not the docsbuild script itself) and I always (by "mistake") built it using "python3 -m venv" when building locally and it always worked perfectly, so the upgrade looks safe.

However as I almost never used salt, I'm still unsure salt is able to upgrade this cleanly, according to the docs a - python: python3 may be enough, if someone knows...