pop duplicates entries when returning downloaded blocks in engine (#3644)

Co-authored-by: Matthias Seitz <matthias.seitz@outlook.de>

crates/consensus/beacon/src/engine/sync.rs

@@ -13,7 +13,7 @@ use reth_stages::{ControlFlow, Pipeline, PipelineError, PipelineWithResult};
 use reth_tasks::TaskSpawner;
 use std::{
     cmp::{Ordering, Reverse},
-    collections::BinaryHeap,
+    collections::{binary_heap::PeekMut, BinaryHeap},
     task::{ready, Context, Poll},
 };
 use tokio::sync::oneshot;
@@ -304,6 +304,14 @@ where
 
         // drain an element of the block buffer if there are any
         if let Some(block) = self.range_buffered_blocks.pop() {
+            // peek ahead and pop duplicates
+            while let Some(peek) = self.range_buffered_blocks.peek_mut() {
+                if peek.0 .0.hash() == block.0 .0.hash() {
+                    PeekMut::pop(peek);
+                } else {
+                    break
+                }
+            }
             return Poll::Ready(EngineSyncEvent::FetchedFullBlock(block.0 .0))
         }