fixed lambda_max error when normalization != sym

[gravins]

gc_lstm, gconv_gru, and gconv_lstm throw an error when normalization is different from "sym". That is due to the fact that ChebConv requires lambda_max values for non-symmetric normalization.

[benedekrozemberczki]

Started the CI/CD, you can push and commit again and see whether it runs.

[codecov-commenter]

Codecov Report

Merging #150 (1a8826f) into master (88480db) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #150   +/-   ##
=======================================
  Coverage   99.31%   99.31%           
=======================================
  Files          57       57           
  Lines        4996     4996           
=======================================
  Hits         4962     4962           
  Misses         34       34           

Impacted Files	Coverage Δ
torch_geometric_temporal/nn/recurrent/gc_lstm.py	100.00% <100.00%> (ø)
torch_geometric_temporal/nn/recurrent/gconv_gru.py	100.00% <100.00%> (ø)
...orch_geometric_temporal/nn/recurrent/gconv_lstm.py	100.00% <100.00%> (ø)

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