core/txpool/blobpool: use nonce from argument instead of tx.Nonce() (#30148)

This does not change the behavior here as the nonce in the argument is
tx.Nonce(). This commit helps to make the function easier to read and avoid
capturing the tx in the function.

core/txpool/blobpool/blobpool.go

@@ -1116,7 +1116,7 @@ func (p *BlobPool) validateTx(tx *types.Transaction) error {
 		ExistingCost: func(addr common.Address, nonce uint64) *big.Int {
 			next := p.state.GetNonce(addr)
 			if uint64(len(p.index[addr])) > nonce-next {
-				return p.index[addr][int(tx.Nonce()-next)].costCap.ToBig()
+				return p.index[addr][int(nonce-next)].costCap.ToBig()
 			}
 			return nil
 		},