ActiveRecord::StaleObjectError: Attempted to update a stale object: MergeRequest.

https://sentry.gitlab.net/gitlab/devgitlaborg/issues/598736/

ActiveRecord::StaleObjectError: Attempted to update a stale object: MergeRequest.
  /opt/gitlab/embedded/service/gitlab-rails/config/initializers/active_record_locking.rb:43:in `_update_record'
    raise ActiveRecord::StaleObjectError.new(self, "update")
  active_record/attribute_methods/dirty.rb:119:in `_update_record'
    partial_writes? ? super(keys_for_partial_write) : super
  active_record/callbacks.rb:306:in `block in _update_record'
    _run_update_callbacks { super }
  active_support/callbacks.rb:126:in `call'
    env.value = !env.halted && (!block || block.call)
  active_support/callbacks.rb:506:in `block (2 levels) in compile'
    final_sequence = CallbackSequence.new { |env| Filters::ENDING.call(env) }
...
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ActiveRecord::StaleObjectError: Attempted to update a stale object: MergeRequest.