Querying managed Prometheus metrics error: json: cannot unmarshal object into Go struct field HttpBody.data of type string about google-api-go-client HOT 5 OPEN

package main

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"path"
	"testing"
	"time"

	monv1 "google.golang.org/api/monitoring/v1"
	"google.golang.org/api/option"
	apihttp "google.golang.org/api/transport/http"
)

func main() {
	fmt.Println("Hello, 世界")
}

const projectID = "XXX"

func TestPromMetrics(t *testing.T) {
	opts := []option.ClientOption{
		option.WithScopes("https://www.googleapis.com/auth/monitoring.read"),
	}
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	targetx := fmt.Sprintf("https://monitoring.googleapis.com/v1/projects/%s/location/global/prometheus", projectID)
	transport, err := apihttp.NewTransport(ctx, http.DefaultTransport, opts...)
	if err != nil {
		t.Fatal("create HTTP transport", "err", err)
	}
	client := http.Client{Transport: transport}
	u, err := url.Parse(targetx)
	if err != nil {
		t.Fatal("parse target URL", "err", err)
	}
	u.Path = path.Join(u.Path, "/api/v1/query_range")
	q := &monv1.QueryRangeRequest{
		Query:   "up",
		Start:   time.Now().UTC().Add(-5 * time.Minute).Format(time.RFC3339),
		End:     time.Now().UTC().Format(time.RFC3339),
		Step:    "60s",
		Timeout: "60s",
		// ForceSendFields: nil,
		// NullFields:      nil,
	}
	body, err := json.Marshal(q)
	if err != nil {
		t.Fatal("marshal query", "err", err)
	}

	newReq, err := http.NewRequestWithContext(ctx, http.MethodPost, u.String(), bytes.NewReader(body))
	resp, err := client.Do(newReq)
	if err != nil {
		t.Fatal("do request", "err", err)
	}
	defer resp.Body.Close()
	res, err := io.ReadAll(resp.Body)
	if err != nil {
		t.Fatal("read response", "err", err)
	}
	t.Log(string(res))
}