fix(alerting): add a proper compare func for location in mute timings (#82153)

pkg/services/ngalert/api/api_alertmanager_guards_test.go

@@ -2,6 +2,7 @@ package api
 
 import (
 	"testing"
+	"time"
 
 	amConfig "github.com/prometheus/alertmanager/config"
 	"github.com/prometheus/alertmanager/pkg/labels"
@@ -563,6 +564,7 @@ func defaultInterval(t *testing.T) []timeinterval.TimeInterval {
 	t.Helper()
 	return []timeinterval.TimeInterval{
 		{
+			Location: &timeinterval.Location{Location: time.Local},
 			Years: []timeinterval.YearRange{
 				{
 					InclusiveRange: timeinterval.InclusiveRange{