NoMethodError in Search::Zoekt::CallbackService

Summary

undefined method `indexed_at=' for nil:NilClass
           repo.indexed_at = Time.current
               ^^^^^^^^^^^^^

Steps to reproduce

TBD

What is the current bug behavior?

The callback service has a null repository when trying to set something on it

ee/app/services/search/zoekt/callback_service.rb

Relevant logs and/or screenshots

https://new-sentry.gitlab.net/organizations/gitlab/issues/956798/?alert_rule_id=13&alert_type=issue&environment=gprd&notification_uuid=e7330dec-35b5-4908-b8de-c6cb4978a06b&project=3

from kibana entry https://log.gprd.gitlab.net/app/discover#/doc/7092c4e2-4eb5-46f2-8305-a7da2edad090/pubsub-rails-inf-gprd-023064?id=P33TCZEBIlkWoZTHC3sm

[index, (empty), {"task_id"=>16354884}, {"repo_stats"=>{"index_file_count"=>1, "size_in_bytes"=>542204}}]

Possible fixes