Do not apply SLA labels when issuable does not support it

ee/app/workers/incident_management/apply_incident_sla_exceeded_label_worker.rb

@@ -9,9 +9,10 @@ module IncidentManagement
 
     def perform(incident_id)
       @incident = Issue.find_by_id(incident_id)
-      @project = incident&.project
+      return unless incident&.supports_severity?
 
-      return unless incident && project
+      @project = incident&.project
+      return unless project
 
       @label = incident_exceeded_sla_label
       return if incident.label_ids.include?(label.id)

ee/spec/workers/incident_management/apply_incident_sla_exceeded_label_worker_spec.rb

@@ -39,4 +39,15 @@ RSpec.describe IncidentManagement::ApplyIncidentSlaExceededLabelWorker do
     expect(event.action).to eq('add')
     expect(event.label).to eq(label)
   end
+
+  context 'for plain issues' do
+    before_all do
+      incident.update!(issue_type: 'issue')
+    end
+
+    it 'does not add a label', :aggregate_failures do
+      expect { subject }.not_to change { incident.labels.reload.count }
+      expect(incident.labels.reload).to be_empty
+    end
+  end
 end