Ensure unique values in fabricators (#29515)

spec/fabricators/identity_fabricator.rb

@@ -3,5 +3,5 @@
 Fabricator(:identity) do
   user { Fabricate.build(:user) }
   provider 'MyString'
-  uid      'MyString'
+  uid { sequence(:uid) { |i| "uid_string_#{i}" } }
 end

spec/fabricators/relay_fabricator.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
 Fabricator(:relay) do
-  inbox_url 'https://example.com/inbox'
+  inbox_url { sequence(:inbox_url) { |i| "https://example.com/inboxes/#{i}" } }
   state :idle
 end

spec/fabricators/site_upload_fabricator.rb

@@ -2,5 +2,5 @@
 
 Fabricator(:site_upload) do
   file { Rails.root.join('spec', 'fabricators', 'assets', 'utah_teapot.png').open }
-  var 'thumbnail'
+  var { sequence(:var) { |i| "thumbnail_#{i}" } }
 end