chore(ui) Allow a Clippy warning.

We want to keep `apply_input` as before. It's no longer async but let's
keep it as is for the moment. That's a possible future clean up.

crates/matrix-sdk-ui/src/room_list_service/mod.rs

@@ -396,6 +396,7 @@ impl RoomListService {
     ///
     /// After some updates, these is no more `Input` but this API is kept in
     /// case of a future necessity.
+    #[allow(clippy::unused_async)]
     pub async fn apply_input(&self, _input: Input) -> Result<InputResult, Error> {
         Ok(InputResult::Ignored)
     }