[`flake8-pyi`] Make example error out-of-the-box (`PYI042`) (#19101)
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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
Part of #18972
This PR makes [snake-case-type-alias
(PYI042)](https://docs.astral.sh/ruff/rules/snake-case-type-alias/#snake-case-type-alias-pyi042)'s
example error out-of-the-box
[Old example](https://play.ruff.rs/8fafec81-2228-4ffe-81e8-1989b724cb47)
```py
type_alias_name: TypeAlias = int
```
[New example](https://play.ruff.rs/b396746c-e6d2-423c-bc13-01a533bb0747)
```py
from typing import TypeAlias
type_alias_name: TypeAlias = int
```
Imports were also added to the "use instead" section.
## Test Plan
<!-- How was it tested? -->
N/A, no functionality/tests affected
ruff
321575e4 - [`flake8-pyi`] Make example error out-of-the-box (`PYI042`) (#19101)
