Sharing some findings, but I'm still far from the solution.

Regarding the first issue with the 2023.1 branch
1) 2023.1 tobiko job using ubuntu-focal nodes
PASS - tox3.28 - python3.8
https://1d99560c221207a33e89-14a854fbbf5a230846aba3c6a65bcd80.ssl.cf5.rackcdn.com/periodic/opendev.org/openstack/neutron/stable/2023.1/devstack-tobiko-neutron/d1de823/job-output.txt
2023-09-13 02:32:25.704782 | TASK [tobiko-ensure-tox : show Tox facts]
2023-09-13 02:32:25.765288 | {'tox_executable': '/usr/bin/python3 -m tox', 'tox_version': '3.28.0 imported from /home/zuul/.local/lib/python3.8/site-packages/tox/__init__.py'}
...
2023-09-13 02:33:41.677560 | controller | neutron_sanity run-test: commands[0] | /home/zuul/src/opendev.org/x/tobiko/.tox/py3/bin/python /home/zuul/src/opendev.org/x/tobiko/tools/run_tests.py /home/zuul/src/opendev.org/x/tobiko/tobiko/tests/sanity/neutron


2) 2023.1 tobiko job using ubuntu-jammy nodes
FAIL - tox3.28 - python3.10
https://storage.bhs.cloud.ovh.net/v1/AUTH_dcaab5e32b234d56b626f72581e3644c/zuul_opendev_logs_583/894857/1/experimental/devstack-tobiko-neutron/5838bf0/job-output.txt
2023-09-13 16:46:17.132141 | TASK [tobiko-ensure-tox : show Tox facts]
2023-09-13 16:46:17.185958 | {'tox_executable': '/usr/bin/python3 -m tox', 'tox_version': '3.28.0 imported from /usr/local/lib/python3.10/dist-packages/tox/__init__.py'}
...
2023-09-13 16:46:20.555843 | controller | ERROR:   neutron_sanity: could not install deps [-c/home/zuul/src/opendev.org/x/tobiko/upper-constraints.txt, -r/home/zuul/src/opendev.org/x/tobiko/requirements.txt, -r/home/zuul/src/opendev.org/x/tobiko/test-requirements.txt, -r/home/zuul/src/opendev.org/x/tobiko/extra-requirements.txt]; v = InvocationError('could not find executable python', None)


3) master tobiko job using ubuntu-jammy nodes
PASS - tox3.28 - python3.10
https://83fd172b39bb4bd8571a-4a42abeb7e7779ef25c6242290fc9b63.ssl.cf2.rackcdn.com/periodic/opendev.org/openstack/neutron/master/devstack-tobiko-neutron/f7ae7d8/job-output.txt
2023-09-15 02:34:39.846829 | TASK [tobiko-ensure-tox : show Tox facts]
2023-09-15 02:34:39.954407 | {'tox_executable': '/usr/bin/python3 -m tox', 'tox_version': '3.28.0 imported from /home/zuul/.local/lib/python3.10/site-packages/tox/__init__.py'}
...
2023-09-15 02:35:29.405645 | controller | neutron_sanity run-test: commands[0] | /home/zuul/src/opendev.org/x/tobiko/.tox/py3/bin/python /home/zuul/src/opendev.org/x/tobiko/tools/run_tests.py /home/zuul/src/opendev.org/x/tobiko/tobiko/tests/sanity/neutron


Comparing 2 and 3, it looks to me like python packages (at least, tox) are installed in different paths and that may be related to the issue:
'3.28.0 imported from /usr/local/lib/python3.10/dist-packages/tox/__init__.py'
versus
'3.28.0 imported from /home/zuul/.local/lib/python3.10/site-packages/tox/__init__.py'

The error raised [1] happens when tox tries to find the path to python:
https://github.com/tox-dev/tox/blob/3.28.0/src/tox/venv.py#L676






Regarding the second issue [2], ubuntu jammy is not a supported version:
https://github.com/openstack/devstack/blob/stable/wallaby/stack.sh#L230
SUPPORTED_DISTROS="bionic|focal|f31|f32|opensuse-15.2|opensuse-tumbleweed|rhel8|rhel9"




[1] InvocationError('could not find executable python', None)
[2] WARNING: this script has not been tested on jammy