[fleet] throw CE on transactor termination

GitOrigin-RevId: c2a70c26a4c2a35f13c13c00e4c14b4df6f8c7c9

fleet/kernel/src/fleet/kernel/Transactor.kt

@@ -395,7 +395,7 @@ suspend fun withTransactor(
             }
             is TransactorEvent.TheEnd -> {
               currentCoroutineContext().ensureActive()
-              throw RuntimeException("Kernel is terminated", event.reason)
+              throw CancellationException("Transactor is terminated", event.reason)
             }
           }
         }