BUG: explicit tz=None ignored in Timestamp constructor

```python
In [14]: Timestamp(datetime(2022, 1, 1, tzinfo=timezone.utc), tz=None)
Out[14]: Timestamp('2022-01-01 00:00:00+0000', tz='UTC')
```

If a user explicitly passes tz=None and a tzaware string or datetime object, we should raise.  This was fixed for DatetimeIndex in GH#48659
