[`flake8-datetimez`] Make `DTZ901` example error out-of-the-box (#19056)
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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
Part of #18972
This PR makes [datetime-min-max
(DTZ901)](https://docs.astral.sh/ruff/rules/datetime-min-max/#datetime-min-max-dtz901)'s
example error out-of-the-box
[Old example](https://play.ruff.rs/c1202727-1a18-4d3f-92a4-334ede07ed3e)
```py
datetime.max
```
[New example](https://play.ruff.rs/af2c76aa-9beb-46bc-8e27-faf53ecdbe8c)
```py
import datetime
datetime.datetime.max
```
I also added imports to the problem demonstration and use instead.
## Test Plan
<!-- How was it tested? -->
N/A, no functionality/tests affected
ruff
8cc14ad0 - [`flake8-datetimez`] Make `DTZ901` example error out-of-the-box (#19056)
