BUG: Index.get_loc always raise InvalidIndexError on listlike
- [ ] closes #xxxx
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [ ] whatsnew entry

Shouldn't be user-facing unless user is using Index.get_loc directly since we catch this in the relevant Series/DataFrame indexing methods.  The upshot here is this will allow us to simplify `Series.__setitem__` (and maybe others)
mypy complaints are unrelated, just opened a PR that should address them