[retiarii] use fixed seeds for unit test of CGO engine (#4361)

test/ut/retiarii/test_cgo_engine.py

@@ -5,6 +5,7 @@ import unittest
 import time
 import torch
 import torch.nn as nn
+from pytorch_lightning.utilities.seed import seed_everything
 
 from pathlib import Path
 
@@ -138,6 +139,8 @@ def _reset():
     nni.retiarii.integration_api._advisor = None
     nni.retiarii.execution.api._execution_engine = None
     
+    seed_everything(42)
+
 
 def _new_trainer():
     transform = transforms.Compose([transforms.ToTensor(), transforms.Normalize((0.1307,), (0.3081,))])