STYLE exclude io from inconsistent namespace check
xref https://github.com/pandas-dev/pandas/pull/40069#issuecomment-786931356

- [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
is this still needed? we merged the patch on master. My thinking was that this'd prevent unnecessary future error messages from the hook, but maybe the correct thing would be to change such objects so they're imported directly from `pandas.io` (as was done in the patch) as that's more explicit anyway - closing then