DOC: fix examples in Timestamp functions
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] 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
- [ ] whatsnew entry

I tried to create a new issue with the issue template 2 times but I got this error each time

![image](https://user-images.githubusercontent.com/23453691/144195459-541b63df-e84f-4a9f-9a90-855b8e68dbce.png)

Anyway, these changes are very small so perhaps there is no need to create an issue. I didn't run any tests since I made the changes through GitHub and did not clone the project locally.
Thanks @valentinoli 