Stabilize tracing in the cancellation timing test (#60882)

Keep a `NoSubscriber` dispatch alive while the cancellation-before-admission
test runs so untraced parallel workers registering the callsite do not
interfere with timing log capture.

GitOrigin-RevId: 11bc60e3e4633d3ccf426823aeb271875affa39a

codex-rs/core/src/tools/parallel.rs

@@ -784,6 +784,8 @@ mod tests {
             .with_max_level(tracing::Level::INFO)
             .with_writer(MockWriter::new(buffer))
             .finish();
+        // An untraced parallel worker can register this callsite before the test does.
+        let _untraced = tracing::Dispatch::new(tracing::subscriber::NoSubscriber::default());
         let _subscriber_guard = tracing::subscriber::set_default(subscriber);
 
         let (session, mut turn_context) = crate::session::tests::make_session_and_context().await;