Fix unstable feature use

Author: flodiebold

crates/hir-ty/src/method_resolution.rs

@@ -589,7 +589,7 @@ pub fn lookup_impl_method(
     let mut table = InferenceTable::new(db, env.clone());
     find_matching_impl(impls, &mut table, &self_ty).and_then(|data| {
         data.items.iter().find_map(|it| match it {
-            AssocItemId::FunctionId(f) => (db.function_data(*f).name == *name).then_some(*f),
+            AssocItemId::FunctionId(f) => (db.function_data(*f).name == *name).then(|| *f),
             _ => None,
         })
     })