Fix `test_tsagcn`

[cshjin]

Fix the issue in #186 Changes

• send edge_index to device
• assign self_mat to device to match edge_index
• passed the pytest

  
  $ pytest test/
  ============================================ test session starts =============================================
  platform linux -- Python 3.7.16, pytest-7.1.2, pluggy-1.0.0
  rootdir: /home/***/pytorch_geometric_temporal
  collected 93 items                                                                                           

test/attention_test.py ........ [ 8%] test/batch_test.py ............................. [ 39%] test/dataset_test.py .......................................... [ 84%] test/heterogeneous_test.py . [ 86%] test/recurrent_test.py ............. [100%]

======================================= 93 passed in 119.87s (0:01:59) =======================================