Fix test_slice: avoid unnecessary copying of TensorArray from subblock to parent block(#30168)

In control flow, don't copy TensorArray from subblock to parent block when TensorArray is created in parent block.

python/paddle/fluid/layers/control_flow.py

@@ -2278,6 +2278,10 @@ def copy_var_to_parent_block(var, layer_helper):
     assert parent_idx >= 0, "Got wrong parent block index when assigning var to parent scope in control_flow"
     parent_block = prog.block(parent_idx)
 
+    if var.type == core.VarDesc.VarType.LOD_TENSOR_ARRAY \
+            and parent_block._find_var_recursive(var.name):
+        parent_block_var = var
+    else:
         parent_block_var = parent_block.create_var(
             dtype=var.dtype, shape=var.shape, type=var.type)
         assign(var, parent_block_var)

python/paddle/fluid/tests/unittests/dygraph_to_static/test_slice.py

@@ -40,9 +40,12 @@ def test_slice_in_if(x):
     if x.numpy()[0] > 0:
         a.append(x)
     else:
-        a.append(paddle.full(shape=[1, 2], fill_value=9, dtype="int64"))
+        a.append(paddle.full(shape=[1, 2], fill_value=9, dtype="int32"))
+
     if x.numpy()[0] > 0:
         a[0] = x
+
+    a[0] = x + 1
     out = a[0]
     return out