core: fix a typo (#24198)

core/blockchain.go

@@ -554,7 +554,7 @@ func (bc *BlockChain) setHeadBeyondRoot(head uint64, root common.Hash, repair bo
 			// Degrade the chain markers if they are explicitly reverted.
 			// In theory we should update all in-memory markers in the
 			// last step, however the direction of SetHead is from high
-			// to low, so it's safe the update in-memory markers directly.
+			// to low, so it's safe to update in-memory markers directly.
 			bc.currentBlock.Store(newHeadBlock)
 			headBlockGauge.Update(int64(newHeadBlock.NumberU64()))
 		}