Verify `LinkNeighborLoader` supports temporal homogeneous graph with an example

[akihironitta]

🚀 The feature, motivation and pitch

• Add test cases for temporal homogeneous graphs if any test cases are missing (contributes to #6528)
• Add an example that uses LinkNeighborLoader with a temporal heterogeneous graph, such as GDELTLite.

Alternatives

No response

Additional context

#7791 fixed edge_label_index being of size [2, batch_size*2] instead of expected [2, batch_size].