Fix db:migrate:multi-version-upgrade jobs for stable branches

In https://gitlab.com/gitlab-org/release/tasks/-/issues/13750, we disabled these jobs using the DISABLE_DB_MULTI_VERSION_UPGRADE pipeline variable because the job was failing on the stable branches.

We should fix the problem so that this does not happen for future stable branch pipelines.

From the investigation in https://gitlab.com/gitlab-org/release/tasks/-/issues/13750#note_2169124058, we may be able to skip these jobs for the stable branches.