switch benchmark to isolate runnable (#54374)

packages/flutter_tools/lib/src/run_hot.dart

diff --git a/packages/flutter_tools/lib/src/run_hot.dart b/packages/flutter_tools/lib/src/run_hot.dart
index 64ac9c0..64bcbca 100644
--- a/packages/flutter_tools/lib/src/run_hot.dart
+++ b/packages/flutter_tools/lib/src/run_hot.dart
@@ -572,7 +572,7 @@
         for (final FlutterView view in device.views) {
           isolateNotifications.add(
             view.owner.vm.vmService.onIsolateEvent.firstWhere((vm_service.Event event) {
-              return event.kind == vm_service.EventKind.kServiceExtensionAdded;
+              return event.kind == vm_service.EventKind.kIsolateRunnable;
             }),
           );
         }