[GraphBolt] mag240M example does not reach expected accuracies.

[mfbalin]

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

Description

Our graphbolt examples need to be able to match the accuracy of the mag240M reference implementation below. However, none of the DGL and the PyG hetero examples can match the 0.7 accuracy achieved in the reference implementation.

https://github.com/dmlc/dgl/tree/master/examples/pytorch/ogb_lsc/MAG240M

[mfbalin]

@frozenbugs @Rhett-Ying