CLN: add typing to dtype arg in core/common.py (GH38808)
Follow the issue - https://github.com/pandas-dev/pandas/issues/38808

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

thanks @tushushu 