Merge branch '414487-remove_defer_on_database_health_signal_check' into 'master'

Add a comment to explain we safely refer defer_on_database_health_signal?

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/157086



Merged-by: Prabakaran Murugesan <pmurugesan@gitlab.com>
Approved-by: Sam Word <sword@gitlab.com>
Approved-by: Hitesh Raghuvanshi <hraghuvanshi@gitlab.com>
Reviewed-by: Alex Ives <aives@gitlab.com>
Reviewed-by: Sam Word <sword@gitlab.com>

lib/gitlab/sidekiq_middleware/skip_jobs.rb

@@ -76,6 +76,8 @@ def run_job_by_ff?(worker_class)
       end
 
       def defer_job_by_database_health_signal?(job, worker_class)
+        # ActionMailer's ActiveJob pushes a job hash with class: ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper
+        # which won't be having :defer_on_database_health_signal? defined
         unless worker_class.respond_to?(:defer_on_database_health_signal?) &&
             worker_class.defer_on_database_health_signal?
           return false