Reduce the complexity of graphs/bi_directional_dijkstra.py (#8165)

* Reduce the complexity of graphs/bi_directional_dijkstra.py

* Try to lower the --max-complexity threshold in the file .flake8

* Lower the --max-complexity threshold in the file .flake8

* updating DIRECTORY.md

* updating DIRECTORY.md

* Try to lower max-complexity

* Try to lower max-complexity

* Try to lower max-complexity

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