Fix a build error

This commit fixes the following build error:
https://github.com/rubocop/rubocop-rails/actions/runs/12994004909/job/36237485832

Author: koic

spec/spec_helper.rb

@@ -15,6 +15,10 @@
 end
 
 RSpec.configure do |config|
+  # TODO: It can be removed when the oldest supported RuboCop version is greater than 1.71.0.
+  # https://github.com/rubocop/rubocop/pull/13748
+  config.include RuboCop::RSpec::ExpectOffense
+
   config.shared_context_metadata_behavior = :apply_to_host_groups
   config.filter_run_when_matching :focus
   config.filter_run_excluding broken_on: :prism if ENV['PARSER_ENGINE'] == 'parser_prism'