Nox installs Python using uv with non-uv backend

[oliversen]

Current Behavior

Nox installs Python using uv with non-uv backend. If uv is installed on the system.

Expected Behavior

Don't use uv to install Python with non-uv backend.

Steps To Reproduce

noxfile.py:

import nox

@nox.session(python="3.8")
def lint(session):
    ...

Invoke nox -s lint.

If Python 3.8 is not installed globally:

nox > Running session lint
Installed Python 3.8.20 in 2m 20s
 + cpython-3.8.20-windows-x86_64-none
nox > Creating virtual environment (virtualenv) using python3.8 in .nox\lint
nox > Command ...\.venv\Scripts\python.exe -m virtualenv '...\.nox\lint' -p python3.8 failed with exit code 1:
RuntimeError: failed to find interpreter for Builtin discover of python_spec='python3.8'
nox > Session lint failed.

If Python 3.8 is installed globally.

nox > Running session lint
Installed Python 3.8.20 in 3m 55s
 + cpython-3.8.20-windows-x86_64-none
nox > Creating virtual environment (virtualenv) using python3.8 in .nox\lint
nox > Session lint was successful.

Nox installed Python using uv. But the Nox session virtual environment uses the globally installed version of Python. Because virtualenv is not compatible with uv.

Environment

- OS: Windows 10
- Python: 3.11
- Nox: 2024.10.9

Anything else?

No response