[chore] move app server tests from chat completion to responses (#8939)

We are deprecating chat completions. Move all app server tests from chat
completion to responses.

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

@@ -37,7 +37,7 @@ model_provider = "mock_provider"
 [model_providers.mock_provider]
 name = "Mock provider for test"
 base_url = "http://127.0.0.1:0/v1"
-wire_api = "chat"
+wire_api = "responses"
 request_max_retries = 0
 stream_max_retries = 0
 {requires_line}