uv in commands does not resolve to the version packaged with tox-uv

[hugovk]

Follow on from https://github.com/tox-dev/tox-uv/issues/16.

I need to hardcode uv pip instead of {envpython} -m pip when using tox-uv:

 commands_pre =
-    {envpython} -m pip install -r requirements.txt
+    uv pip install -r requirements.txt

This works on:

• Ubuntu: CPython 3.8-3.13
• macOS: CPython 3.8-3.10

This does not work on:

• macOS: CPython 3.11-3.13

py: commands_pre[0]> uv pip install -r requirements.txt
py: failed with uv is not allowed, use allowlist_externals to allow it

With regular tox, I don't need to allowlist pip.