BUG: pd.read_json May Not Maintain Numeric String Index
- [x] closes #28556
- [x] tests added / passed
- [ ] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Hello @theoniko! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2021-01-04 22:32:49 UTC All requested changes were made. Please re-review the pr. merge master as well lgtm pushed a small doc change and can merge on green