BUG: unstack with object dtype of tzaware timestamps
- [ ] closes #xxxx
- [x] tests added / passed
- [x] 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

this is ok for 1.3, can you rebase @meeseeksdev backport 1.3.x Something went wrong ... Please have  a look at my logs. It seems that it's not fixed for the case where mask_all is true. I'll send another PR
https://github.com/pandas-dev/pandas/blob/42082a80d0c3b3483f08b887271b1b08c66551e1/pandas/core/reshape/reshape.py#L294