update xpu zero dim tensor ut (#50289)

* xpu scatter ut no backward

* update gather xpu ut

python/paddle/fluid/tests/unittests/xpu/test_zero_dim_tensor_xpu.py

@@ -583,42 +583,35 @@ def test_gather_xD_axis_0(self):
         self.assertEqual(x.grad.shape, [2, 3])
         self.assertEqual(out.grad.shape, [3])
 
-    def _test_gather_xD_axis_1(self):
+    def test_gather_xD_axis_1(self):
         x = paddle.to_tensor(
             [[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]], stop_gradient=False
         )
         index = paddle.full([], 1, 'int64')
         out = paddle.gather(x, index, axis=1)
-        out.backward()
 
         self.assertEqual(out.shape, [2])
         np.testing.assert_array_equal(out.numpy(), [2.0, 5.0])
-        self.assertEqual(x.grad.shape, [2, 3])
-        self.assertEqual(out.grad.shape, [2])
 
-    def _test_scatter_1D(self):
+    def test_scatter_1D(self):
         x = paddle.to_tensor([1.0, 3.0, 5.0, 7.0, 9.0], stop_gradient=False)
         index = paddle.full([], 2, 'int64')
         updates = paddle.full([], 4.0)
         out = paddle.scatter(x, index, updates)
-        out.backward()
 
         self.assertEqual(out.shape, [5])
         self.assertEqual(out.numpy()[2], 4)
-        self.assertEqual(out.grad.shape, [5])
 
-    def _test_scatter_XD(self):
+    def test_scatter_XD(self):
         x = paddle.to_tensor(
             [[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]], stop_gradient=False
         )
         index = paddle.full([], 1, 'int64')
         updates = paddle.to_tensor([1.0, 2.0, 3.0])
         out = paddle.scatter(x, index, updates)
-        out.backward()
 
         self.assertEqual(out.shape, [2, 3])
         np.testing.assert_array_equal(out.numpy()[1], [1.0, 2.0, 3.0])
-        self.assertEqual(out.grad.shape, [2, 3])
 
     def test_diagflat(self):
         x1 = paddle.rand([])