Omit previous error from Sidekiq JSON logs

Sidekiq stores a job's error details in the payload for the _next_ run,
so that it can display the error in the Sidekiq UI. This is because
Sidekiq's main state is the queue of jobs to be run. However, in our
logs, this is very confusing, because we shouldn't have any error at all
when a job starts, and we already add an error message and class to our
logs when a job fails.

changelogs/unreleased/omit-previous-error-from-sidekiq-logs.yml

+---
+title: Omit error details from previous attempt in Sidekiq JSON logs
+merge_request: 25161
+author:
+type: changed

lib/gitlab/sidekiq_logging/structured_logger.rb

@@ -77,7 +77,9 @@ module Gitlab
       end
 
       def parse_job(job)
-        job = job.dup
+        # Error information from the previous try is in the payload for
+        # displaying in the Sidekiq UI, but is very confusing in logs!
+        job = job.except('error_backtrace', 'error_class', 'error_message')
 
         # Add process id params
         job['pid'] = ::Process.pid

spec/lib/gitlab/sidekiq_logging/structured_logger_spec.rb

@@ -18,7 +18,10 @@ describe Gitlab::SidekiqLogging::StructuredLogger do
         "jid" => "da883554ee4fe414012f5f42",
         "created_at" => created_at.to_f,
         "enqueued_at" => created_at.to_f,
-        "correlation_id" => 'cid'
+        "correlation_id" => 'cid',
+        "error_message" => "wrong number of arguments (2 for 3)",
+        "error_class" => "ArgumentError",
+        "error_backtrace" => []
       }
     end
 
@@ -26,7 +29,7 @@ describe Gitlab::SidekiqLogging::StructuredLogger do
     let(:clock_thread_cputime_start) { 0.222222299 }
     let(:clock_thread_cputime_end) { 1.333333799 }
     let(:start_payload) do
-      job.merge(
+      job.except('error_backtrace', 'error_class', 'error_message').merge(
         'message' => 'TestWorker JID-da883554ee4fe414012f5f42: start',
         'job_status' => 'start',
         'pid' => Process.pid,