Update src/concurrency/thread.rs

Co-authored-by: Ralf Jung <[email protected]>

Author: shamb0

src/concurrency/thread.rs

@@ -63,7 +63,7 @@ pub type DyMachineCallback<'tcx> = Box<dyn MachineCallback<'tcx> + 'tcx>;
 #[macro_export]
 macro_rules! callback {
     (@capture<$tcx:lifetime $(,)? $($lft:lifetime),*> { $($name:ident: $type:ty),* $(,)? }
-     @unblock = |$this:ident, $result:ident| $complete:expr $(,)?)
+     @unblock = |$this:ident, $arg:ident| $body:expr $(,)?)
     => {{
 
         struct Callback<$tcx, $($lft),*> {