Incorrect default value for python-preference in docs/reference/settings.md

[FishAlchemist]

According to #5637 , the default value in the document should be changed to "only-managed" because the managed behavior requires --preview. However, if the document is intended for post-stabilization behavior (without --preview), it should also be changed to "managed" instead of using a removed value.
I'm not sure which one should be changed to so I won't create a PR for it

uv/docs/reference/settings.md

Line 646 in 257007c

**Default value**: `"installed"`

uv/crates/uv-python/src/discovery.rs

Lines 61 to 69 in 257007c

	pub enum PythonPreference {
	/// Only use managed Python installations; never use system Python installations.
	OnlyManaged,
	#[default]
	/// Prefer managed Python installations over system Python installations.
	///
	/// System Python installations are still preferred over downloading managed Python versions.
	/// Use `only-managed` to always fetch a managed Python version.
	Managed,

Edit (according to my PR):
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.

[charliermarsh]

Apologies, this changed recently. PR welcome. We can include both the stable and preview value in the default field.