BUG: frame._item_cache not cleared when Series is altered
- [x] closes #33675
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

lgtm. ok for 1.1.2 i think. any perf implications? > any perf implications?

I dont think so.  It's just a dict.pop, and any case when its hit is one where we're doing the wrong thing now. thanks @jbrockmendel  @meeseeksdev backport 1.1.x