Fix antenna fabricator tests and move duplicate check to db

db/migrate/20230822041804_add_antenna_elements_uniqueness.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require Rails.root.join('lib', 'mastodon', 'migration_helpers')
+
+class AddAntennaElementsUniqueness < ActiveRecord::Migration[7.0]
+  include Mastodon::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def change
+    safety_assured do
+      add_index :antenna_accounts, [:antenna_id, :account_id], unique: true
+      add_index :antenna_domains, [:antenna_id, :name], unique: true
+      add_index :antenna_tags, [:antenna_id, :tag_id], unique: true
+    end
+  end
+end