error[E0597]: `userdata` does not live long enough
  --> $DIR/userdata_borrow.rs:15:25
   |
15 |         _userdata_ref = userdata.borrow::<MyUserData>();
   |                         ^^^^^^^^ borrowed value does not live long enough
16 |         //~^ error: `userdata` does not live long enough
17 |     }
   |     - `userdata` dropped here while still borrowed
18 |     Ok(())
19 | }
   | - borrow might be used here, when `_userdata_ref` is dropped and runs the destructor for type `std::result::Result<std::cell::Ref<'_, main::MyUserData>, mlua::error::Error>`
   |
   = note: values in a scope are dropped in the opposite order they are defined