BUG: `Styler.to_latex` with multirow cellcolor
- [x] xref #41994 but provides an alternative workable solution.
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] No whatsnew entry needed since `apply_index` methods were added in 1.4.0 and this bug fix is an extension to that.
