Fix setting share_with_group_lock

What does this MR do?

This fixes Namespace#force_share_with_group_lock_on_descendants so it doesn't update all namespaces instead of just the descendants. For more information see the following issues:

• https://gitlab.com/gitlab-org/gitlab-ce/issues/37916
• https://gitlab.com/gitlab-com/infrastructure/issues/2773

Thanks to @_stark for finding the underlying query that lead to us identifying what code caused this.

This has to be picked into the next available RC.

cc @rspeicher @jarka

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together