Fix /admin/tags/:id crashing since Rails 6.1 update (#15953)

Raw SQL passed to `pluck` now has to be explicitly marked as SQL via
Arel.sql, see https://github.com/rails/rails/pull/27947

app/controllers/admin/tags_controller.rb

@@ -59,8 +59,8 @@ module Admin
                              .where(Status.arel_table[:id].gteq(Mastodon::Snowflake.id_at(Time.now.utc.beginning_of_day)))
                              .joins(:account)
                              .group('accounts.domain')
-                             .reorder('statuses_count desc')
-                             .pluck('accounts.domain, count(*) AS statuses_count')
+                             .reorder(statuses_count: :desc)
+                             .pluck(Arel.sql('accounts.domain, count(*) AS statuses_count'))
     end
 
     def set_counters