Silence lint false positive (#2989)
When running the `uv-client` tests, i would previously get:
```
warning: field `0` is never read
--> crates/uv-configuration/src/config_settings.rs:43:27
|
43 | pub struct ConfigSettings(BTreeMap<String, ConfigSettingValue>);
| -------------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| field in this struct
|
= note: `ConfigSettings` has derived impls for the traits `Clone` and `Debug`, but these are intentionally ignored during dead code analysis
= note: `#[warn(dead_code)]` on by default
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
|
43 | pub struct ConfigSettings(());
| ~~
warning: `uv-configuration` (lib) generated 1 warning
```
