Don't use end_time when comparing payloads

- Ensures we match on two payloads with differing end_times
- Fixes where alert without explicit fingerprint could not be resolved

ee/lib/ee/gitlab/alerting/notification_payload_parser.rb

@@ -6,7 +6,7 @@ module EE
       module NotificationPayloadParser
         extend ::Gitlab::Utils::Override
 
-        EXCLUDED_PAYLOAD_FINGERPRINT_PARAMS = %w(start_time hosts).freeze
+        EXCLUDED_PAYLOAD_FINGERPRINT_PARAMS = %w(start_time end_time hosts).freeze
 
         # Currently we use full payloads, when generating a fingerprint.
         # This results in a quite strict fingerprint.

ee/spec/services/projects/alerting/notify_service_spec.rb

@@ -51,6 +51,28 @@ RSpec.describe Projects::Alerting::NotifyService do
         it 'increments the existing alert count' do
           expect { subject }.to change { existing_alert.reload.events }.from(1).to(2)
         end
+
+        context 'end_time provided for subsequent alert' do
+          before do
+            payload[:end_time] = Time.current.change(usec: 0).iso8601
+          end
+
+          let(:existing_alert) do
+            existing_payload =  payload.except(:end_time)
+            described_class.new(project, nil, existing_payload).execute(token)
+
+            AlertManagement::Alert.last!
+          end
+
+          it 'does not create AlertManagement::Alert' do
+            expect { subject }.not_to change(AlertManagement::Alert, :count)
+          end
+
+          it 'resolves the existing alert', :aggregate_failures do
+            expect { subject }.to change { existing_alert.reload.resolved? }.from(false).to(true)
+            expect(existing_alert.ended_at).to eq(payload[:end_time])
+          end
+        end
       end
     end
   end