DOC: Fix error in pandas.Index.to_series
- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Related to #27977. 

output of `python scripts/validate_docstrings.py pandas.Index.to_series`:
```
################################################################################
################################## Validation ##################################
################################################################################
```

Notes:
While working with the documentation, I noticed that index parameter in `pandas.Index.to_series` has different behaviour with `pandas.Index.to_frame`. You can't specify index parameter to False in `pandas.Index.to_series` to achieve the same index result with `pandas.Index.to_frame`. Is this intentional?

