BUG: Ensure df.itertuples() uses plain tuples correctly
Currently DataFrame.itertuples() has an off by one error
when it inspects whether or not it should return namedtuples
or plain tuples in it's response.

This PR addresses that bug by correcting the condition
that is used when making the check.

Closes: #28282

- [x] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
