tests(core): re-enable pending input follow-up coverage

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/tests/suite/pending_input.rs

@@ -45,7 +45,6 @@ fn message_input_texts(body: &Value, role: &str) -> Vec<String> {
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-#[ignore = "TODO(aibrahim): flaky"]
 async fn injected_user_input_triggers_follow_up_request_with_deltas() {
     let (gate_completed_tx, gate_completed_rx) = oneshot::channel();