TST: raise InvalidIndexError with IntervalIndex.get_value and get_loc
ensure InvalidIndexError is raised when non-scalar is passed as key to
get_loc and get_value methods for IntervalIndex

- [X] closes #31117 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
