[rust-lang/rust] `unused_features` triggers on stable `lint_reasons` despite usage

### ROOT CAUSE The `unused_features` lint incorrectly flags the `lint_reasons` feature as unused, even though it's required for the `reason` attribute. This is because the `lint_reasons` feature is stable (stabilized in Rust 1.66.0) and does not need to be gated in stable Rust. The presence of `#![feature(lint_reasons)]` triggers the lint, but the feature is already available. ### CODE FIX Remove the `#![feature(lint_reasons)]` attribute since `lint_reasons` is stable and does not require gating. The `reason` attribute will still work because it's part of the stable language. **Fixed Code:** ```rust #![deny(warnings)] #[allow(unused_variables, reason = "my reason")] fn main() { let x = (); } ```