BUG: preserve timezone info when writing empty tz-aware series to HDF5 
- [x] closes #20594 (coupled with #37069 for empty tz-aware dataframes)
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

xref #20595 (stale PR that looked into this)