feat(cargo-lints): Add feature gates to lint groups

Author: Muscraft

src/cargo/util/lints.rs

@@ -220,13 +220,15 @@ pub struct LintGroup {
     pub default_level: LintLevel,
     pub desc: &'static str,
     pub edition_lint_opts: Option<(Edition, LintLevel)>,
+    pub feature_gate: Option<&'static Feature>,
 }
 
 const TEST_DUMMY_UNSTABLE: LintGroup = LintGroup {
     name: "test_dummy_unstable",
     desc: "test_dummy_unstable is meant to only be used in tests",
     default_level: LintLevel::Allow,
     edition_lint_opts: None,
+    feature_gate: Some(Feature::test_dummy_unstable()),
 };
 
 #[derive(Copy, Clone, Debug)]