Bug in Series constructor returning wrong missing values
- [x] closes #43017
- [x] xref #43018 (if the reindex case is ok, then this is done too)
- [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 ensures consistency with the DataFrame constructor