Hacking and Testing instructions no longer works

[Guillaume Beuzeboc]

If I reproduce the steps from the HACKING.md and TESTING.md I can no longer run the static and unit tests.

The steps from HACKING.md to setup the test containers are:
- ./tools/environment-setup.sh
- lxc exec snapcraft-dev -- sudo -iu ubuntu bash

This works ok.
Then the instructions in TESTING.md:
- make tests-static
- make test-units
  They both give:

(snapcraft) ubuntu@snapcraft-dev:~/snapcraft$ make tests-static
tox run -e lint-black
ROOT: will run in automatically provisioned tox, host /home/ubuntu/.venv/snapcraft/bin/python3 is missing [requires (has)]: tox==4.4.6 (4.0.11), tox-ignore-env-name-mismatch==0.2.0.post2
Traceback (most recent call last):
  File "/home/ubuntu/.venv/snapcraft/bin/tox", line 8, in <module>
    sys.exit(run())
  File "/home/ubuntu/.venv/snapcraft/lib/python3.8/site-packages/tox/run.py", line 19, in run
    result = main(sys.argv[1:] if args is None else args)
  File "/home/ubuntu/.venv/snapcraft/lib/python3.8/site-packages/tox/run.py", line 41, in main
    result = provision(state)
  File "/home/ubuntu/.venv/snapcraft/lib/python3.8/site-packages/tox/provision.py", line 124, in provision
    return run_provision(provision_tox_env, state)
  File "/home/ubuntu/.venv/snapcraft/lib/python3.8/site-packages/tox/provision.py", line 142, in run_provision
    tox_env: PythonRun = cast(PythonRun, state.envs[name])
  File "/home/ubuntu/.venv/snapcraft/lib/python3.8/site-packages/tox/session/env_select.py", line 317, in __getitem__
    return self._defined_envs[item].env
  File "/home/ubuntu/.venv/snapcraft/lib/python3.8/site-packages/tox/session/env_select.py", line 181, in _defined_envs
    run_env = self._build_run_env(name)
  File "/home/ubuntu/.venv/snapcraft/lib/python3.8/site-packages/tox/session/env_select.py", line 242, in _build_run_env
    runner = REGISTER.runner(cast(str, env_conf["runner"]))
  File "/home/ubuntu/.venv/snapcraft/lib/python3.8/site-packages/tox/tox_env/register.py", line 72, in runner
    return self._run_envs[name]
KeyError: 'ignore_env_name_mismatch'
make: *** [Makefile:14: test-black] Error 1