fix(open_ai): add `xhigh` to list of supported reasoning effort values

Kunall Banerjee created

According to the
[docs](https://platform.openai.com/docs/api-reference/chat/create#chat_create-reasoning_effort),
`xhigh` is a supported value for all models after `gpt-5.1-codex-max`.

Change summary

crates/settings/src/settings_content/language_model.rs | 1 +
1 file changed, 1 insertion(+)

Detailed changes