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

thanks @jbrockmendel  whatsnew in 1.1.2. should this be backported and milestone changed or release note moved?

in release readiness I now check whatsnew on master and backport in sync

https://github.com/simonjayhawkins/pandas-release/runs/1078142445?check_suite_focus=true @meeseeksdev backport 1.1.x
