(TST) Replacing Timestamp.now () in tests.
- [x] xref #44341
- [ ] 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

Replacing Timestamp.now() in tests.
Left Timestamp.now () in the following tests:

```
scalar/timestamp/test_timestamp.py:290:        compare(Timestamp.now(), datetime.now())
scalar/timestamp/test_timestamp.py:291:        compare(Timestamp.now("UTC"), datetime.now(timezone("UTC")))
scalar/timestamp/test_timestamp.py:320:        compare(Timestamp.now(), datetime.now())
scalar/timestamp/test_timestamp.py:321:        compare(Timestamp.now("UTC"), datetime.now(tzutc()))
scalar/timestamp/test_constructors.py:480:        ts_from_method = Timestamp.now()
scalar/timestamp/test_constructors.py:484:        ts_from_method_tz = Timestamp.now(tz="US/Eastern")
```
  

Hello @Mikhaylov-yv! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:















































There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2021-11-20 18:47:30 UTC Does this cover all the non-intentional cases of `now()`? @mroeschke 

> Does this cover all the non-intentional cases of `now()`?

Yes it covers all cases.

Where I was in doubt left `now()` @mroeschke Oh sure. But I don’t understand how to do it. No problem can you merge master one more time @Mikhaylov-yv ? @mroeschke yes of course.  Thanks @Mikhaylov-yv. CI failures unrelated 