create two mrs in project in the same time shows 500 error

Summary

when create mr it shows 500 error, the prodution.log shows here:

Steps to reproduce

create two mrs in project in the same time

Relevant logs and/or screenshots

ActiveRecord::RecordNotUnique Mysql2::Error: Duplicate entry '16084-9915' for key 'index_merge_requests_on_target_project_id_and_iid': INSERT INTO
`merge_requests`