simulators/ethereum/engine: fix loop variable override

[MariusVanDerWijden]

The "Out of Order Payload Execution (go-ethereum)" test fails with this panic. I think it is because of this line

hive/simulators/ethereum/engine/enginetests.go

Line 1190 in 82fd6c4

r := secondaryTestEngineClients[i].TestEngineNewPayloadV1(&payload)

which probably accesses the engine client array out of bounds. We overwrote the i value in the inner loop

panic: runtime error: index out of range [10] with length 1

goroutine 536 [running]:
github.com/ethereum/hive/hivesim.runTest.func2.1()
	/go/pkg/mod/github.com/ethereum/hive@v0.0.0-20220216101708-2784ea3e7eea/hivesim/testapi.go:327 +0x7b
panic({0x839740, 0xc0000260c0})
	/usr/local/go/src/runtime/panic.go:838 +0x207
main.outOfOrderPayloads(0xc000220630)
	/source/enginetests.go:1190 +0x9aa
main.RunTest({0x86da77, 0x1e}, 0xb?, 0xc0001a8f70?, 0xc00002c5c0, 0xc000362410, 0x89b8e0, 0xc0003229f0, 0xc000322330)
	/source/testenv.go:127 +0x668
main.main.func1(0xc00002c5c0?, 0xc0004042f0?)
	/source/main.go:142 +0xc9
github.com/ethereum/hive/hivesim.ClientTestSpec.runTest.func1(0x0?)
	/go/pkg/mod/github.com/ethereum/hive@v0.0.0-20220216101708-2784ea3e7eea/hivesim/testapi.go:359 +0xa6
github.com/ethereum/hive/hivesim.runTest.func2()
	/go/pkg/mod/github.com/ethereum/hive@v0.0.0-20220216101708-2784ea3e7eea/hivesim/testapi.go:333 +0x71
created by github.com/ethereum/hive/hivesim.runTest
	/go/pkg/mod/github.com/ethereum/hive@v0.0.0-20220216101708-2784ea3e7eea/hivesim/testapi.go:323 +0x2ca

[marioevz]

LGTM