Add test to AR's counter_cache_test.rb

According to
https://github.com/rails/rails/blob/b601399b72ab56cc01368f02615af99f45d1
4f02/activerecord/lib/active_record/counter_cache.rb#L14, u can pass
more then one association to the `reset_counters` method.
Fix tests which started to fail due to commit 0123c39f41e2062311b2197e6e230ef8ad67e20e

Due to commit 0123c39f41e2062311b2197e6e230ef8ad67e20e, column
topic.unique_replies_count has been added, and these test started to
fail since the tests depends on the topic tables column info.
Merge pull request #10676 from tkhr/add-test-to-counter_cache_test.rb

Add test to counter cache test.rb