automation: make system3 the default for run-tests-linux
We'll soon drop support for Python 2.7. Let's use Python 3 by
default.
Differential Revision: https://phab.mercurial-scm.org/D12261
automation: run hg with python3
Python 2.7 support will go away soon. Let's use Python 3 as part of
the automation.
Differential Revision: https://phab.mercurial-scm.org/D12260
Simon Sapin <simon.sapin@octobus.net> [Thu, 03 Mar 2022 07:53:11 +0100] rev 48842
rust: enable Python 3 support unconditionally
Note: `cpython/python3-sys` is a default feature.
Differential Revision: https://phab.mercurial-scm.org/D12316