Fix alerts with evaluation interval more than 30 seconds resolving in Alertmanager (#39513) (#39523)

(cherry picked from commit 27609dc2c5)

Co-authored-by: George Robinson <george.robinson@grafana.com>

pkg/services/ngalert/state/state.go

@@ -158,7 +158,7 @@ func (a *State) TrimResults(alertRule *ngModels.AlertRule) {
 func (a *State) setEndsAt(alertRule *ngModels.AlertRule, result eval.Result) {
 	ends := ResendDelay
 	if alertRule.IntervalSeconds > int64(ResendDelay.Seconds()) {
-		ends = time.Duration(alertRule.IntervalSeconds)
+		ends = time.Second * time.Duration(alertRule.IntervalSeconds)
 	}
 
 	a.EndsAt = result.EvaluatedAt.Add(ends * 3)

pkg/services/ngalert/state/state_test.go

@@ -149,14 +149,14 @@ func TestSetEndsAt(t *testing.T) {
 		},
 		{
 			name:     "more than resend delay: for=unset,interval=1m - endsAt = interval * 3",
-			expected: evaluationTime.Add(60 * 3),
+			expected: evaluationTime.Add(time.Second * 60 * 3),
 			testRule: &ngmodels.AlertRule{
 				IntervalSeconds: 60,
 			},
 		},
 		{
 			name:     "more than resend delay: for=0s,interval=1m - endsAt = resendDelay * 3",
-			expected: evaluationTime.Add(60 * 3),
+			expected: evaluationTime.Add(time.Second * 60 * 3),
 			testRule: &ngmodels.AlertRule{
 				For:             0 * time.Second,
 				IntervalSeconds: 60,
@@ -164,7 +164,7 @@ func TestSetEndsAt(t *testing.T) {
 		},
 		{
 			name:     "more than resend delay: for=1m,interval=5m - endsAt = interval * 3",
-			expected: evaluationTime.Add(300 * 3),
+			expected: evaluationTime.Add(time.Second * 300 * 3),
 			testRule: &ngmodels.AlertRule{
 				For:             60 * time.Second,
 				IntervalSeconds: 300,
@@ -172,7 +172,7 @@ func TestSetEndsAt(t *testing.T) {
 		},
 		{
 			name:     "more than resend delay: for=5m,interval=1m - endsAt = interval * 3",
-			expected: evaluationTime.Add(60 * 3),
+			expected: evaluationTime.Add(time.Second * 60 * 3),
 			testRule: &ngmodels.AlertRule{
 				For:             300 * time.Second,
 				IntervalSeconds: 60,