fix(protocol): approval policy never prompt (#11288)

This removes overly directed language about how the model should behave
when it's in `approval_policy=never` mode.

---------

Co-authored-by: Dylan Hurd <dylan.hurd@openai.com>

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

@@ -72,7 +72,7 @@ async fn build_codex_with_test_tool(server: &wiremock::MockServer) -> anyhow::Re
 fn assert_parallel_duration(actual: Duration) {
     // Allow headroom for slow CI scheduling; barrier synchronization already enforces overlap.
     assert!(
-        actual < Duration::from_millis(1_200),
+        actual < Duration::from_millis(1_600),
         "expected parallel execution to finish quickly, got {actual:?}"
     );
 }