fix: test yield time (#5811)

Author: jif-oai

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

@@ -240,7 +240,7 @@ async fn unified_exec_emits_output_delta_for_exec_command() -> Result<()> {
     let call_id = "uexec-delta-1";
     let args = json!({
         "cmd": "printf 'HELLO-UEXEC'",
-        "yield_time_ms": 250,
+        "yield_time_ms": 1000,
     });
 
     let responses = vec![