Rails 5: fix presence message validation for prometheus_alert

ee/changelogs/unreleased/rails5-fix-prometheus-alert-event-spec.yml

+---
+title: 'Rails 5: fix presence message validation for prometheus_alert'
+merge_request: 7823
+author: Jasper Maes
+type: other

ee/spec/models/prometheus_alert_event_spec.rb

@@ -13,7 +13,7 @@ describe PrometheusAlertEvent do
   describe 'validations' do
     it { is_expected.to be_valid }
 
-    it { is_expected.to validate_presence_of(:prometheus_alert) }
+    it { is_expected.to validate_presence_of(:prometheus_alert).with_message(Gitlab.rails5? ? :required : :blank ) }
     it { is_expected.to validate_uniqueness_of(:payload_key).scoped_to(:prometheus_alert_id) }
     it { is_expected.to validate_presence_of(:started_at) }