op-e2e: fix tx-gossip flake (#10692)

op-e2e/l2_gossip_test.go

 package op_e2e
 
 import (
+	"math/big"
 	"testing"
+	"time"
 
 	"github.com/ethereum-optimism/optimism/op-e2e/e2eutils/geth"
 	"github.com/ethereum/go-ethereum/common"
@@ -23,6 +25,10 @@ func TestTxGossip(t *testing.T) {
 	verifClient := sys.Clients["verifier"]
 	geth.ConnectP2P(t, seqClient, verifClient)
 
+	// This prevents the below tx-sending from flaking in CI
+	_, err = geth.WaitForBlock(big.NewInt(10), verifClient, time.Minute)
+	require.NoError(t, err)
+
 	// Send a transaction to the verifier and it should be gossiped to the sequencer and included in a block.
 	SendL2Tx(t, cfg, verifClient, cfg.Secrets.Alice, func(opts *TxOpts) {
 		opts.ToAddr = &common.Address{0xaa}