miner: discard interrupted blocks (#24638)

During mining, when a new head arrives and interrupts the block building, the block being built should not be commited (but discarded). Committing the interrupted block introduces unnecessary delay, and possibly causes miner to mine on the previous head, which could result in higher uncle rate.

eth/catalyst/api_test.go

@@ -108,7 +108,7 @@ func TestEth2AssembleBlockWithAnotherBlocksTxs(t *testing.T) {
 	api := NewConsensusAPI(ethservice)
 
 	// Put the 10th block's tx in the pool and produce a new block
-	api.insertTransactions(blocks[9].Transactions())
+	api.eth.TxPool().AddRemotesSync(blocks[9].Transactions())
 	blockParams := beacon.PayloadAttributesV1{
 		Timestamp: blocks[8].Time() + 5,
 	}