Fix the default value of python-preference in docs/reference/settings.md

[FishAlchemist]

Summary

After referring to #5637 and doing additional testing.
The default value in a stable state seems more reasonable to be only-system. managed in preview.

cpython-3.11.9-windows-x86_64-none     C:\Users\name\AppData\Local\Programs\Python\Python311\python.exe

cpython-3.10.14-windows-x86_64-none    C:\Users\name\AppData\Roaming\uv\data\python\cpython-3.10.14-windows-x86_64-none\install\python.exe
cpython-3.10.11-windows-x86_64-none    C:\Users\name\AppData\Local\Programs\Python\Python310\python.exe

cpython-3.9.19-windows-x86_64-none     C:\Users\name\AppData\Roaming\uv\data\python\cpython-3.9.19-windows-x86_64-none\python.exe

test on uv 0.2.33 (build from https://github.com/astral-sh/uv/tree/257007ccaf0912a41dfe91b534527a7b1f54e19a)

Stable version

uv venv -p 3.10 is 3.10.11 (System Python)
uv venv -p 3.9 is No interpreter found(3.9.19 for managed Python)
uv venv -p 3.9 --python-preference only-system is No interpreter found(fail)
uv venv -p 3.9 --python-preference only-managed is 3.9.19(success)
Do not use managed Python, only use the system Python, so it can be determined as only-system.

Preview mode

Note: 3.10.14 is managed python, 3.10.11 is system python.
uv venv -p 3.11 --preview is 3.11.9 (System Python)
uv venv -p 3.10 --preview is 3.10.14
uv venv -p 3.10 --preview --python-preference only-managed is 3.10.14
uv venv -p 3.10 --preview --python-preference managed is 3.10.14
uv venv -p 3.10 --preview --python-preference system is 3.10.11
venv -p 3.10 --preview --python-preference only-system is 3.10.11
Prioritize the managed Python and then select the system Python, so it can be determined as managed.

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fixed #5754

Test Plan

Run website in local.

[zanieb]

Hey! This file is generated. I think you'd need to fix it in the definition itself?

[charliermarsh]

I gotcha. Thanks!