fix check

src/frontend/src/scheduler/distributed/query.rs

@@ -309,7 +309,7 @@ impl QueryRunner {
             );
         }
         // To convince the compiler that `pinned_snapshot` will only be dropped once.
-        let mut pinned_snapshot_to_drop = Some(pinned_snapshot);
+        let pinned_snapshot_to_drop = Some(pinned_snapshot);
 
         let mut finished_stage_cnt = 0usize;
         while let Some(msg_inner) = self.msg_receiver.recv().await {