Write use-uv = true in no-prompt mode

[charliermarsh]

Summary

Ensures that if the user runs in InstallMode::NoPrompts, we still write the default (use-uv = true) to the configuration file.

Closes #1081.

Test Plan

rye on  charlie/def:main
❯ cargo run self install -y
    Finished dev [unoptimized + debuginfo] target(s) in 0.08s
     Running `target/debug/rye self install -y`
Welcome to Rye!

This installer will install rye to /Users/crmarsh/.rye
This path can be changed by exporting the RYE_HOME environment variable.

Details:
  Rye Version: 0.34.0
  Platform: macos (aarch64)

Installed binary to /Users/crmarsh/.rye/shims/rye
Updated self-python installation at /Users/crmarsh/.rye/self

The rye directory /Users/crmarsh/.rye/shims was not detected on PATH.
It is highly recommended that you add it.
Added to PATH.
note: for this to take effect you will need to restart your shell or run this manually:

    source "$HOME/.rye/env"

To make it work with zsh, you might need to add this to your .zprofile:

    source "$HOME/.rye/env"

To make it work with fish, run this once instead:

    set -Ua fish_user_paths "$HOME/.rye/shims"

For more information read https://rye-up.com/guide/installation/

All done!
rye on  charlie/def:main
❯ cat /Users/crmarsh/.rye/config.toml
[behavior]
use-uv = true
global-python = true