Mark flutter_engine_group_performance not flaky (#75892)

dev/prod_builders.json

diff --git a/dev/prod_builders.json b/dev/prod_builders.json
index 0742792..5d52d3e 100644
--- a/dev/prod_builders.json
+++ b/dev/prod_builders.json
@@ -160,7 +160,7 @@
          "name": "Linux flutter_engine_group_performance",
          "repo": "flutter",
          "task_name": "linux_flutter_engine_group_performance",
-         "flaky": true
+         "flaky": false
       },
       {
          "name": "Linux flutter_gallery__back_button_memory",