Handle multiple owners in notification service

app/models/project.rb

@@ -1519,6 +1519,10 @@ class Project < ApplicationRecord
     group || namespace.try(:owner)
   end
 
+  def owners
+    Array.wrap(owner)
+  end
+
   def first_owner
     obj = owner
 

ee/app/services/ee/notification_service.rb

@@ -121,7 +121,7 @@ module EE
     end
 
     def incident_management_owners(project)
-      return [project.owner] unless project.group
+      return project.owners if project.personal?
 
       MembersFinder
         .new(project, nil, params: { active_without_invites_and_requests: true })