add ignore for new mypy error 'type-var'
A new error introduced to mypy is detected in pandas' repository. This PR adds comment to ignore that error.

> pandas (https://github.com/pandas-dev/pandas)
> + pandas/core/resample.py:208: error: A function returning TypeVar should receive at least one argument containing the same Typevar  [type-var]
> + pandas/core/resample.py:208: note: Error code "type-var" not covered by "type: ignore" comment

Reference:
https://github.com/python/mypy/pull/13166

- [ ] [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.
Thank you @anilbey! Sure @twoertwein, happy to help :)