DOC: skip a doctest that writes to disk
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Running `./scripts/validate_docstrings.py` was returning the following error 
```
Exception: The following files were leftover from the doctest: {'formatted_file.xlsx'}. Please use # doctest: +SKIP
```
This was due to the doctest writing to disk. This PR fixes this issue.

thx @moisan