Fix errors for test_standalone_custom_stream (#50103)

python/paddle/fluid/tests/unittests/standalone_executor/test_standalone_custom_stream.py

@@ -50,10 +50,10 @@ class TestCustomStream(unittest.TestCase):
         ops = prog.global_block().ops
         for op_index in op_index_for_stream1:
             ops[op_index].dist_attr.execution_stream = "s1"
-            ops[op_index].dist_attr.stream_priority = -1
+            ops[op_index].dist_attr.stream_priority = 0
         for op_index in op_index_for_stream2:
             ops[op_index].dist_attr.execution_stream = "s2"
-            ops[op_index].dist_attr.stream_priority = -2
+            ops[op_index].dist_attr.stream_priority = -1
 
     def run_program(self, apply_custom_stream=False):
         paddle.seed(2022)