DOC: Fix EX03
Error EX03 has cleaned.

pandas.errors.CategoricalConversionWarning

<img width="470" alt="image" src="https://github.com/pandas-dev/pandas/assets/77875500/d007f149-24f0-478c-b2fb-c32be2039bcc">

pandas.errors.ChainedAssignmentError

<img width="395" alt="image" src="https://github.com/pandas-dev/pandas/assets/77875500/3d7b7c4c-4900-42a6-846f-977bcd621c31">

pandas.errors.ClosedFileError

<img width="356" alt="image" src="https://github.com/pandas-dev/pandas/assets/77875500/c0e4dd3d-79ad-4d27-89cf-25042decfc0f">

pandas.errors.NumExprClobberingError

<img width="391" alt="image" src="https://github.com/pandas-dev/pandas/assets/77875500/acbc09fa-35cf-4790-8d30-f02b47a089a5">

- [ ] xref #56804 (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
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] 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.
Thanks @luke396 