Add unit tests to binary_tree_path_sum.py (#11833)

* test: Add unit tests

* test: Add successful tests in binaree_tree_path_sum

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Update binary_tree_path_sum.py

* Update binary_tree_path_sum.py

* Update binary_tree_path_sum.py

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Maxim Smolskiy <[email protected]>