fix tests for 2018

Author: nikomatsakis

src/test/ui/async-await/issues/issue-64391-2.rs

@@ -4,6 +4,9 @@
 // `"".to_string()` value was causing a (spurious) unwind path that
 // led us to believe that the future might be dropped after `config`
 // had been dropped. This cannot, in fact, happen.
+//
+// check-pass
+// edition:2018
 
 async fn connect() {
     let config = 666;

src/test/ui/async-await/issues/issue-64433.rs

@@ -4,6 +4,7 @@
 // same PR.
 //
 // check-pass
+// edition:2018
 
 #[derive(Debug)]
 struct A<'a> {