Fix `Rails/ReversibleMigration` cop for `change_column` (#30835)

db/migrate/20160223164502_make_uris_nullable_in_statuses.rb

@@ -1,7 +1,11 @@
 # frozen_string_literal: true
 
 class MakeUrisNullableInStatuses < ActiveRecord::Migration[4.2]
-  def change
+  def up
     change_column :statuses, :uri, :string, null: true, default: nil
   end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
 end

db/migrate/20170322143850_change_primary_key_to_bigint_on_statuses.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class ChangePrimaryKeyToBigintOnStatuses < ActiveRecord::Migration[5.0]
-  def change
+  def up
     change_table(:statuses, bulk: true) do |t|
       t.change :id, :bigint
       t.change :reblog_of_id, :bigint
@@ -16,4 +16,8 @@ class ChangePrimaryKeyToBigintOnStatuses < ActiveRecord::Migration[5.0]
     change_column :statuses_tags, :status_id, :bigint
     change_column :stream_entries, :activity_id, :bigint
   end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
 end

db/migrate/20170609145826_remove_default_language_from_statuses.rb

@@ -1,7 +1,11 @@
 # frozen_string_literal: true
 
 class RemoveDefaultLanguageFromStatuses < ActiveRecord::Migration[5.1]
-  def change
+  def up
     change_column :statuses, :language, :string, default: nil, null: true
   end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
 end