BUG: Fix multi-index colname references in read_csv c engine.
This fixes an issue with the read_csv c engine when the input has more than one header row and arguments to dtype, na_values, or converters reference multi-index column names as tuples.

- [x] closes #42446
- [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

I added a whatsnew entry for v1.4.0 since that's what other recent bug fixes have done, but I'm not yet sure of the criteria for that. Is it appropriate to add it for whichever release "owns" master?