[GraphBolt] Default value of `persistent_workers` should be `False`

## 🔨Work Item

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Project tracker: https://github.com/orgs/dmlc/projects/2

## Description
As `gb.DataLoader` inherits from `torch.utils.data.DataLoader`(https://pytorch.org/docs/stable/data.html#torch.utils.data.DataLoader), the default value of `persistent_workers` should be same. But for now, we're using `True` while torch uses `False`.

## Depending work items or issues