Geo: Investigate MR creation failures after 12.8.1 to 12.9.10 upgrade

Upgrade issue: #208104 (closed)

After multi-node Geo setup was upgraded from 12.8.1 to 12.9.10, attempts to create MRs return a 500 error. Calls to the MR API also return 500 error.

Example pipelines:

https://gitlab.com/gitlab-org/quality/looping-pipeline/-/pipelines/158197492 https://gitlab.com/gitlab-org/quality/looping-pipeline/-/pipelines/158175864