[docs][python] Fix return types in docstrings (#5326)
[docs][python] Fix return types in docstrings (#5326)

Update basic.py
microsoft/LightGBM,henry0312/LightGBM,henry0312/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM