REGR: Check for float in isnaobj_old
- [x] closes #35493
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Looks like we lost an isinstance check that caused this regression.
thanks @dsaxton  backport to 1.1.x @simonjayhawkins hmm these don't seem to be triggering a backport action. any idea? > @simonjayhawkins hmm these don't seem to be triggering a backport action. any idea?

it worked on #35452 but not from #35272 @MeeseeksDev backport to 1.1.x