False positive for `await_holding_refcell_ref`

I tried this code:

let mut state = self.state.borrow_mut();
let handles = state.cancel_all_in_flight();
drop(state);
let to_cancel = handles.len();
let cancelled = stream::iter(handles).then(|f| f).count().await;

I expected to see this happen: No error since the RefMut is explicitly dropped before the await

Instead, this happened: Brought up a warning

This happens in the recently promoted beta.

This should be pretty easy to fix. As a short term mitigation, I will downgrade the check from correctness and should hopefully be able to work on the fix next week.

Reproduce the supplied Rust example with the await_holding_refcell_ref lint enabled, then trace that lint's implementation and existing regression tests in rust-clippy. The fix is complete when an explicitly dropped RefMut before the await no longer produces the warning, while the lint still catches a borrow held across await.