Fix deprecators for Rails 7.1

What does this MR do and why?

Rails.application.deprecators are used in Rails 7.1 instead of ActiveSupport::Deprecation

• https://handbook.gitlab.com/handbook/engineering/architecture/design-documents/rails_upgrade/
• Move test fixes out of the Rails 7.1 Upgrade MR (#475085 - closed)

Verify

BUNDLE_GEMFILE=Gemfile.next bundle exec rspec spec/lib/gitlab_spec.rb:384 raises significantly less warnings after the commit rather than before the commit