Make the defaulted trait object lifetime bounds in allow_threads expl…

…icit to make the transmute call more obvious.

src/marker.rs

@@ -336,7 +336,7 @@ impl<'py> Python<'py> {
         // access thread-local storage from the current thread.
 
         // 1. Construct a task
-        struct Task(*mut dyn FnMut());
+        struct Task(*mut (dyn FnMut() + 'static));
         unsafe impl Send for Task {}
 
         let (result_sender, result_receiver) = sync_channel::<Result<T>>(0);
@@ -356,7 +356,7 @@ impl<'py> Python<'py> {
         };
 
         // SAFETY: the current thread will block until the closure has returned
-        let mut task = Task(unsafe { transmute(&mut task as &mut dyn FnMut()) });
+        let mut task = Task(unsafe { transmute(&mut task as &mut (dyn FnMut() + '_)) });
 
         // 2. Dispatch task to waiting thread, spawn new thread if necessary
         let trap = PanicTrap::new(