fix: typos in model picker (#6859)

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codex-rs/app-server/tests/suite/set_default_model.rs

@@ -57,7 +57,7 @@ fn create_config_toml(codex_home: &Path) -> std::io::Result<()> {
     std::fs::write(
         config_toml,
         r#"
-model = "gpt-5.1-codex"
+model = "arcticfox"
 model_reasoning_effort = "medium"
 "#,
     )