BUG: to_hdf append string column to incompatible column
- [ ] closes #xxxx
- [X] 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
- [X] whatsnew entry

Hello @lrepiton! 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 2021-06-14 08:17:47 UTC thanks @lrepiton  @meeseeksdev backport 1.3.x Something went wrong ... Please have  a look at my logs.