Update _json.py
Without this change, use of the chunksize argument in read_json causes the following error:

`TypeError: initial_value must be str or None, not bytes`

- [x] closes #28906
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
