Call pending_migrations once

This was accidentally calling pending_migrations twice, and while
probably not a big deal, there's no reason to.

Author: eileencodes

activerecord/lib/active_record/migration.rb

@@ -682,8 +682,10 @@ def disable_ddl_transaction!
       end
 
       def check_pending_migrations # :nodoc:
-        if pending_migrations.any?
-          raise ActiveRecord::PendingMigrationError.new(pending_migrations: pending_migrations)
+        migrations = pending_migrations
+
+        if migrations.any?
+          raise ActiveRecord::PendingMigrationError.new(pending_migrations: migrations)
         end
       end