DEPR: treating float data as wall-times in DTA._from_sequence
- [ ] closes #xxxx
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

Oops looks like this one slipped through the cracks. Care to merge main one more time? green Thanks @jbrockmendel 