FIX: Disable auto_update for existent themes (#11244)

db/migrate/20201116132948_set_themes_auto_update_false.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class SetThemesAutoUpdateFalse < ActiveRecord::Migration[6.0]
+  def up
+    execute "UPDATE themes SET auto_update = false"
+  end
+
+  def down
+    execute "UPDATE themes SET auto_update = true"
+  end
+end