error[E0597]: `var` does not live long enough
  --> tests/async_compile_fail/captured_variable.rs:9:23
   |
7  |     let fut = {
   |         --- borrow later stored here
8  |         let mut var = 1u32;
   |             ------- binding `var` declared here
9  |         let var_ref = &mut var;
   |                       ^^^^^^^^ borrowed value does not live long enough
...
13 |     };
   |     - `var` dropped here while still borrowed