The time drifts in timer store in daylight saving time

[lcwangchao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

The below test will fail:

func TestTimerStoreWithDST(t *testing.T) {
	store := testkit.CreateMockStore(t)
	tk := testkit.NewTestKit(t, store)
	dbName := "test"
	tblName := "timerstore"
	tk.MustExec("use test")
	tk.MustExec(tablestore.CreateTimerTableSQL(dbName, tblName))
	tk.MustExec("set @@time_zone = 'America/Los_Angeles'")

	pool := pools.NewResourcePool(func() (pools.Resource, error) {
		return tk.Session(), nil
	}, 1, 1, time.Second)
	defer pool.Close()

	timerStore := tablestore.NewTableTimerStore(1, pool, dbName, tblName, nil)
	defer timerStore.Close()

	watermark, err := time.ParseInLocation(time.DateTime, "2024-11-03 09:30:00", time.UTC)
	require.NoError(t, err)

	id, err := timerStore.Create(context.TODO(), &api.TimerRecord{
		TimerSpec: api.TimerSpec{
			Namespace:       "default",
			Key:             "test",
			SchedPolicyType: api.SchedEventInterval,
			SchedPolicyExpr: "1h",
			Watermark:       watermark,
		},
	})
	require.NoError(t, err)

	timer, err := timerStore.GetByID(context.TODO(), id)
	require.NoError(t, err)
	// this assert will fail
	require.Equal(t, watermark.In(time.UTC).String(), timer.Watermark.In(time.UTC).String())
}

2. What did you expect to see? (Required)

test success

3. What did you see instead (Required)

--- FAIL: TestTimerStoreWithDST (2.53s)

Expected :2024-11-03 09:30:00 +0000 UTC
Actual   :2024-11-03 08:30:00 +0000 UTC

4. What is your TiDB version? (Required)