[v9.3.x] Alerting: Fix integration test for creating silences (#65791)

Alerting: Fix integration test for creating silences (#65722)

* fix integration test for creating silences

to create correct silence with endsAt in the future

* Update api_alertmanager_test.go

(cherry picked from commit ed8628e39d)

Co-authored-by: Yuri Tseretyan <yuriy.tseretyan@grafana.com>

pkg/tests/api/alerting/api_alertmanager_test.go

@@ -12,11 +12,12 @@ import (
 	"testing"
 	"time"
 
-	"github.com/grafana/grafana/pkg/expr"
 	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
+	"github.com/grafana/grafana/pkg/expr"
+
 	apimodels "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
 	ngmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
 	ngstore "github.com/grafana/grafana/pkg/services/ngalert/store"
@@ -208,11 +209,11 @@ func TestIntegrationAMConfigAccess(t *testing.T) {
 	})
 
 	t.Run("when creating silence", func(t *testing.T) {
-		body := `
+		now := time.Now()
+		body := fmt.Sprintf(`
 		{
 			"comment": "string",
 			"createdBy": "string",
-			"endsAt": "2023-03-31T14:17:04.419Z",
 			"matchers": [
 			  {
 				"isRegex": true,
@@ -220,9 +221,10 @@ func TestIntegrationAMConfigAccess(t *testing.T) {
 				"value": "string"
 			  }
 			],
-			"startsAt": "2021-03-31T13:17:04.419Z"
+			"startsAt": "%s",
+			"endsAt": "%s"
 		  }
-		`
+		`, now.Format(time.RFC3339), now.Add(10*time.Second).Format(time.RFC3339))
 
 		testCases := []testCase{
 			{