Place test with async-await and use 2018 edition

Author: jonhoo

src/test/ui/fmt/issue-64477.rs renamed to src/test/ui/async-await/issues/issue-64477-2.rs

@@ -1,8 +1,14 @@
+// Another regression test for #64477.
+//
 // In the past, the code generated by `format!` produced temporaries in the surrounding scope that
 // borrowed the arguments through `&dyn Trait`. These temporaries do not implement `Send`, which
 // meant that when `format!` was used in an async block, the resulting generator was not `Send`.
 // See https://github.com/rust-lang/rust/issues/64477#issuecomment-534669068 for details
 // and https://github.com/rust-lang/rust/issues/64477#issuecomment-531882958 for an example.
+//
+// check-pass
+// edition:2018
+
 async fn foo(_: String) {}
 
 fn bar() -> impl Send {