Fixed docstring error with style.py, unknown parameter: {'text_color_threshold'}
When you run python` ./scripts/validate_docstrings.py --errors=PR02`, one of the errors is `/home/pandas/pandas/io/formats/style.py:3144:PR02:pandas.io.formats.style.Styler.text_gradient:Unknown parameters {'text_color_threshold'}`

The error I believe was because the function text_gradient was using the doc-string for background gradient, which had text_color_threshold as one of the parameters, so validate doc-string expected text_gradient to also have text_color_threshold, even though that parameter was not intended for text_gradient.

- [X] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
this looks good pending the checks and also have you rendered the docs, does it all display OK? Hi, I don't believe the changes I have made, contributed to the errors in the checks. Could you please clarify? Thanks @joshuabello2550