Bug in iloc.setitem orienting IntegerArray into the wrong direction
- [x] closes #40933
- [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

This is more or less a follow up of #39040, so don't think we need a whatsnew?