REGR: Resampler.aggregate fails when used with column selection
- [x] closes #42905
- [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
- [x] whatsnew entry

The method `resample._GroupByMixin._gotitem` calls

```
new_rs = type(self)(
    subset, groupby=groupby, parent=self, selection=selection, **kwargs
)
```

The selection (which ends up in kwargs in `__init__`) was being ignored.
