fix parallel ssa graph executor test hang; test=develop (#25358)

python/paddle/fluid/tests/unittests/test_parallel_executor_fetch_isolated_var.py

@@ -27,7 +27,7 @@ class TestParallelExecutorFetchIsolatedVarBase(unittest.TestCase):
     def build_network(self, is_training):
         x = fluid.data(name='x', shape=[-1, 10], dtype='float32')
         y = fluid.data(name='y', shape=[-1, 10], dtype='float32')
-        fc = fluid.layers.fc(x, size=30)
+        fc = fluid.layers.fc(x, size=30, bias_attr=False)
         loss = fluid.layers.reduce_mean(fc)
         if is_training:
             adam = fluid.optimizer.Adam(learning_rate=1e-3)