Follow-up from "Replace ci_runners with partitioned table"

The following discussion from !183508 (merged) should be addressed:

  • @tianwenchen started a discussion:

    async_nullify conflicts with non-nullable column definition of ci_running_builds.runner_id

Related to the incident reported at https://gitlab.slack.com/archives/CNZ8E900G/p1745891877926459?thread_ts=1745891329.184099&cid=CNZ8E900G

Edited by Tianwen Chen