[Rails5] undefined method `cast_type' for #<ActiveRecord::ConnectionAdapters::PostgreSQLColumn:0x000056538062c968>

Note: add rails5 to a branch name to trigger rails5 specific CI jobs.

https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/73736426

  6) WebHookLog should serialize :response_headers class_name => Hash
     Failure/Error: it { is_expected.to serialize(:response_headers).as(Hash) }

     NoMethodError:
       undefined method `cast_type' for #<ActiveRecord::ConnectionAdapters::PostgreSQLColumn:0x000056538062c968>
     # ./spec/models/hooks/web_hook_log_spec.rb:8:in `block (2 levels) in <top (required)>'