Fix doc for Neovim setting examples (#18491)
## Summary
This PR fixes an error in the example Neovim configuration on [this
documentation
page](https://docs.astral.sh/ruff/editors/settings/#configuration).
The `configuration` block should be nested under `settings`, consistent
with other properties and as outlined
[here](https://docs.astral.sh/ruff/editors/setup/#neovim).
I encountered this issue when copying the example to configure ruff
integration in my neovim - the config didn’t work until I corrected the
nesting.
## Test Plan
- [x] Confirmed that the corrected configuration works in a real Neovim
+ Ruff setup
- [x] Verified that the updated configuration renders correctly in
MkDocs
<img width="382" alt="image"
src="https://github.com/user-attachments/assets/0722fb35-8ffa-4b10-90ba-c6e8417e40bf"
/>
