Bogus deprecation warning on find_or_create_by

[ojab]

Steps to reproduce

AFAIU unscoped behaviour will be default one in 6.1, but right now there is no way to force it, so deprecation warning is essentially unfixable.
See brendon/acts_as_list#363 for example.

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", github: "rails/rails"
  gem "sqlite3"
end

require "active_record"
require "minitest/autorun"
require "logger"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.text :text
  end
end

class Post < ActiveRecord::Base
  after_save :acts_as_list

  def acts_as_list
    Post.unscope(:where)
  end
end

ActiveSupport::Deprecation.behavior = :raise

class BugTest < Minitest::Test
  def test_association_stuff
    Post.find_or_create_by!(text: 'text')
  end
end

Expected behavior

No deprecation warning

Actual behavior

ActiveSupport::DeprecationException: DEPRECATION WARNING: Class level methods will no longer inherit scoping from create!in Rails 6.1. To continue using the scoped relation, pass it into the block directly. To instead access the full set of models, as Rails 6.1 will, usePost.unscoped, or Post.default_scoped if a model has default scopes. (called from acts_as_list at active_record_master.rb:32)

System configuration

Rails version: 6.0 or git master

Ruby version: 2.6.5

[ojab]

Maybe we can do if scope.present? here, but I'm not sure if it's a correct fix.

[kamipo]

Related #38241.

Use default_scoped in this case for 6.1 migration to avoid leaking scope. #38319