cl: fix for periodic retry of not-ready response (#18374) (#18376)

cherry-pick of #18374

---

when exec responds with !ready (say due to pruning) Caplin should try
again before it gives up

that seems to be the intent in the code but the implementation has a bug
- it uses a `Timer` instead of a `Ticker`

we're getting missed (orphaned) blocks due to this

Author: taratorio

cl/phase1/stages/chain_tip_sync.go

@@ -22,7 +22,7 @@ func waitForExecutionEngineToBeFinished(ctx context.Context, cfg *Cfg) (ready bo
 
 	// Setup the timers
 	readyTimeout := time.NewTimer(10 * time.Second)
-	readyInterval := time.NewTimer(50 * time.Millisecond)
+	readyInterval := time.NewTicker(50 * time.Millisecond)
 
 	// Ensure the timers are stopped to release resources
 	defer readyTimeout.Stop()