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

for more information, see https://pre-commit.ci

Author: pre-commit-ci[bot]

data_structures/binary_tree/red_black_tree.py

@@ -863,6 +863,7 @@ def main() -> None:
     >>> pytests()
     """
     import doctest
+
     failures, _ = doctest.testmod()
     if failures == 0:
         print("All doctests passed!")