error: future cannot be shared between threads safely
  --> $DIR/sync-future-impossible.rs:16:32
   |
16 |       async fn method(&mut self) {
   |  ________________________________^
17 | |         println!("{}", self.value);
18 | |     }
   | |_____^ future created by async block is not `Sync`
   |
note: captured value is not `Sync`
  --> $DIR/sync-future-impossible.rs:17:24
   |
17 |         println!("{}", self.value);
   |                        ^^^^ has type `&mut Struct<T>` which is not `Sync`
   = note: required for the cast to the object type `dyn Future<Output = ()> + Send + Sync`
help: consider further restricting this bound
   |
14 | impl<T: std::fmt::Display + Send + Sync> Trait for Struct<T> {
   |                                  ^^^^^^