core/services/vrf/v2: mock SubscribeToHeads to avoid test race (#22053)

Author: jmank88

core/services/vrf/v2/integration_v2_test.go

@@ -3,6 +3,7 @@ package v2_test
 import (
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"math"
 	"math/big"
@@ -2131,6 +2132,7 @@ func TestStartingCountsV1(t *testing.T) {
 	ec.On("ConfiguredChainID").Return(testutils.SimulatedChainID)
 	ec.On("BalanceAt", mock.Anything, mock.Anything, mock.Anything).Maybe().Return(big.NewInt(0), nil)
 	ec.On("LatestBlockHeight", mock.Anything).Return(big.NewInt(2), nil).Maybe()
+	ec.On("SubscribeToHeads", mock.Anything).Maybe().Return(nil, nil, errors.ErrUnsupported)
 	txm := makeTestTxm(t, txStore, ks.Eth(), ec)
 	legacyChains := evmtest.NewLegacyChains(t, evmtest.TestChainOpts{
 		KeyStore:       ks.Eth(),