STYLE enable pylint: overridden-final-method
Issue #48855. This PR enables pylint type "W" warning: `overridden-final-method`
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).

The only occurrence of the warning is in `test_external_block.py`. I think it was made on purpose and disabled the warning on this line.
thanks @natmokval - `mypy` already deals with this one, so I think it might also make sense to keep this one off Thanks, @MarcoGorelli . Didn't know that. I close the PR.