Change src/test to tests in source files, fix tidy and tests

compiler/rustc_trait_selection/src/traits/project.rs

@@ -282,7 +282,7 @@ fn project_and_unify_type<'cx, 'tcx>(
     };
     debug!(?normalized, ?obligations, "project_and_unify_type result");
     let actual = obligation.predicate.term;
-    // For an example where this is necessary see src/test/ui/impl-trait/nested-return-type2.rs
+    // For an example where this is necessary see tests/ui/impl-trait/nested-return-type2.rs
     // This allows users to omit re-mentioning all bounds on an associated type and just use an
     // `impl Trait` for the assoc type to add more bounds.
     let InferOk { value: actual, obligations: new } =