Race between BroadCastPendingBlock and Mining

[AskAlexSharov]

`go test -v -race -run=TestMiningBenchmark .

==================
WARNING: DATA RACE
Write at 0x00c00265e6b0 by goroutine 5739:
  runtime.slicecopy()
      /usr/lib/go-1.24/src/runtime/slice.go:355 +0x0
  github.com/erigontech/erigon/polygon/bor.(*Bor).Seal()
      /home/erigon/erigon/polygon/bor/bor.go:1220 +0x673
  github.com/erigontech/erigon/eth/stagedsync.SpawnMiningFinishStage()
      /home/erigon/erigon/eth/stagedsync/stage_mining_finish.go:111 +0x10c9
  github.com/erigontech/erigon/eth/stagedsync.MiningStages.func10()
      /home/erigon/erigon/eth/stagedsync/stagebuilder.go:92 +0x147
  github.com/erigontech/erigon/eth/stagedsync.(*Sync).runStage()
      /home/erigon/erigon/eth/stagedsync/sync.go:529 +0x3ee
  github.com/erigontech/erigon/eth/stagedsync.(*Sync).StageState()
      /home/erigon/erigon/eth/stagedsync/sync.go:256 +0x3c4
  github.com/erigontech/erigon/eth/stagedsync.(*Sync).runStage()
      /home/erigon/erigon/eth/stagedsync/sync.go:524 +0x2e4
  github.com/erigontech/erigon/eth/stagedsync.(*Sync).Run()
      /home/erigon/erigon/eth/stagedsync/sync.go:412 +0x55c


Previous read at 0x00c00265e6b0 by goroutine 47:
  runtime.slicecopy()
      /usr/lib/go-1.24/src/runtime/slice.go:355 +0x0
  bytes.(*Buffer).Write()
      /usr/lib/go-1.24/src/bytes/buffer.go:181 +0x118
  github.com/erigontech/erigon-lib/rlp.EncodeString()
      /home/erigon/erigon/erigon-lib/rlp/encode.go:666 +0x247
  github.com/erigontech/erigon-lib/types.(*Header).EncodeRLP()
      /home/erigon/erigon/erigon-lib/types/block.go:271 +0x6be
  github.com/erigontech/erigon-lib/types.(*Block).EncodeRLP()
      /home/erigon/erigon/erigon-lib/types/block.go:1233 +0x1b7
  github.com/erigontech/erigon/turbo/privateapi.(*MiningServer).BroadcastPendingBlock()
      /home/erigon/erigon/turbo/privateapi/mining.go:137 +0x94
  github.com/erigontech/erigon/eth.New.func14()
      /home/erigon/erigon/eth/backend.go:988 +0x652

[VBulikov]

VBulikov added Imp2 as Importance