seeding is now idempotent

db/seeds.rb

@@ -67,19 +67,19 @@ unless Rails.env.test?
     end
   end
 
-  OrganisationRelationship.create!(
+  OrganisationRelationship.find_or_create_by!(
     child_organisation: org,
     parent_organisation: housing_provider1,
   )
-  OrganisationRelationship.create!(
+  OrganisationRelationship.find_or_create_by!(
     child_organisation: org,
     parent_organisation: housing_provider2,
   )
-  OrganisationRelationship.create!(
+  OrganisationRelationship.find_or_create_by!(
     child_organisation: managing_agent1,
     parent_organisation: org,
   )
-  OrganisationRelationship.create!(
+  OrganisationRelationship.find_or_create_by!(
     child_organisation: managing_agent2,
     parent_organisation: org,
   )