CI: Added unselected directories to doctest CI
Some of those do have docstrings with example to be validated, and some do not have.

This only make sure that future files or changes to files in those directories will be checked.

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- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
