CLN: pandas/core/indexing.py
- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Slight clean-up of ``pandas/core/indexing.py``.

- Use ``suppress`` instead of ``try/except/pass`` (starting from Python 3.7)
- Slight rearrangement of statements
- Extract method ``_validate_key_length``
LGTM pending green.

If you're looking for high-value things to do in this file, narrowing what we're catching/suppressing is a never-ending battle. Lgtm  Can anyone re-start CI? Looks like there were internal CI engine failures. thanks @ivanovmg nice cleanup