Fix some tests related to Rails 7.1 Upgrade

What does this MR do and why?

Related:

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

Fixes:

• Call the registered parser for rendered content
• Rename builds partials to jobs
• Fix preview_path= deprecation warning
• Fix omniauth callbacks controller tests
• Use Rails.application.deprecators instead of ActiveSupport::Deprecation
• Fix undefined usage_type for GroupDeployKey
• Verify null_relation? instead of ActiveRecord::NullRelation inheritance