eager global detach 接口行为错误

[wyg1997]

Summary

eager global 下 detach 接口获得结果的 autograd 属性不符合预期，影响后续后向图构图。

Code to reproduce bug

cuda_placement = flow.placement("cuda", [0, 1])
cpu_placement = flow.placement("cpu", [0, 1])
B = flow.sbp.broadcast

a = flow.ones(2, 3).to_global(cuda_placement, B)  # cuda placement 才能复现，cpu placement 没问题
if flow.env.get_rank() == 0:
    print(f"{a.is_leaf=}")  # True

b = a.float().clone().detach()
if flow.env.get_rank() == 0:
    print(f"{b.is_leaf=}")  # False but expect True