rpc: use stable object in notifier test (#30193)

This makes the test resilient to changes of types.Header -- otherwise the test needs to be
updated each time the header structure is modified.

rpc/subscription_test.go

@@ -267,13 +267,9 @@ func TestNotify(t *testing.T) {
 		sub:       &Subscription{ID: id},
 		activated: true,
 	}
-	msg := &types.Header{
-		ParentHash: common.HexToHash("0x01"),
-		Number:     big.NewInt(100),
-	}
-	notifier.Notify(id, msg)
+	notifier.Notify(id, "hello")
 	have := strings.TrimSpace(out.String())
-	want := `{"jsonrpc":"2.0","method":"_subscription","params":{"subscription":"test","result":{"parentHash":"0x0000000000000000000000000000000000000000000000000000000000000001","sha3Uncles":"0x0000000000000000000000000000000000000000000000000000000000000000","miner":"0x0000000000000000000000000000000000000000","stateRoot":"0x0000000000000000000000000000000000000000000000000000000000000000","transactionsRoot":"0x0000000000000000000000000000000000000000000000000000000000000000","receiptsRoot":"0x0000000000000000000000000000000000000000000000000000000000000000","logsBloom":"0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000","difficulty":null,"number":"0x64","gasLimit":"0x0","gasUsed":"0x0","timestamp":"0x0","extraData":"0x","mixHash":"0x0000000000000000000000000000000000000000000000000000000000000000","nonce":"0x0000000000000000","baseFeePerGas":null,"withdrawalsRoot":null,"blobGasUsed":null,"excessBlobGas":null,"parentBeaconBlockRoot":null,"hash":"0xe5fb877dde471b45b9742bb4bb4b3d74a761e2fb7cb849a3d2b687eed90fb604"}}}`
+	want := `{"jsonrpc":"2.0","method":"_subscription","params":{"subscription":"test","result":"hello"}}`
 	if have != want {
 		t.Errorf("have:\n%v\nwant:\n%v\n", have, want)
 	}