409 response when removing users form subgroups

Summary

Some customers rely on delete billable members API to remove inactive users from their group. The recent change in this MR cause the existing working user removal script to return 409 {message: 409 Conflict: Resource lock} error. The change was to prevent accidental deletion of the last owner of a group. However, also cause some blockage when removing users from subgroup/project.

For more context see: https://gitlab.com/gitlab-com/dev-sub-department/section-dev-request-for-help/-/issues/32.

Steps to reproduce

Example Project

What is the current bug behavior?

Removing users doesn't isn't blocked with 409 error if the user isn't the last owner of the group.

What is the expected correct behavior?

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

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Results of GitLab application Check

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