Testing to_datetime, converting none to NaT
Addition of a test. Bug was fixed for #35888 somewhere in the main branch, this test just adds a unit test. 

- [x] closes #35888
- [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
- [ ] whatsnew entry (not sure if applicable here, can someone advise?) 
