BUG: Adjust truncate for decreasing index
- [x] closes #33756
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

ping on green > ping on green

@jreback Added tests and green (tests got a little verbose but couldn't think of more succinct wording)  kk thanks