db: fix migration to drop ai_tags.tag_id index concurrently.

Fix deadlock in production when trying to drop this index.

db/migrate/20220627211714_add_tag_id_and_score_index_to_ai_tags.rb

@@ -1,6 +1,8 @@
 class AddTagIdAndScoreIndexToAITags < ActiveRecord::Migration[7.0]
+  disable_ddl_transaction!
+
   def change
     add_index :ai_tags, [:tag_id, :score], if_not_exists: true
-    remove_index :ai_tags, :tag_id
+    remove_index :ai_tags, :tag_id, algorithm: :concurrently, if_exists: true
   end
 end