[python] use f-strings for concatenation in examples/python-guide/advanced_example.py (#4386)
[python] use f-strings for concatenation in examples/python-guide/advanced_example.py (#4386)

* Improved the syntax of the fstrings

* Improved the strings to fstrings

* Reverted back the white space.

* Update examples/python-guide/advanced_example.py

Co-authored-by: Nikita Titov <31eaea17affb14e78210388fc0bace3c2fd52ddc@mail.ru>

Co-authored-by: Nikita Titov <31eaea17affb14e78210388fc0bace3c2fd52ddc@mail.ru>
henry0312/LightGBM,henry0312/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM,microsoft/LightGBM,henry0312/LightGBM,microsoft/LightGBM