Reset status cache when status_stat or media_attachment updates (#9119)

* Reset status cache when status_stat or media_attachment updates

Fix #8711

Media attachments are generally immutable, but admins can update
the sensitive flag, and this would ensure the change is visible
instantly. Same for updates to status stats. That is a regression
from #8185, because even the correct updated_at fetched from a join
doesn't seem to invalidate the cache.

* Remove join from Status#cache_ids since it has no effect

app/models/status_stat.rb

@@ -14,4 +14,12 @@
 
 class StatusStat < ApplicationRecord
   belongs_to :status, inverse_of: :status_stat
+
+  after_commit :reset_parent_cache
+
+  private
+
+  def reset_parent_cache
+    Rails.cache.delete("statuses/#{status_id}")
+  end
 end