Fix rubocop offence for Style/ClassAndModuleChildrenNested for PushRule controllers

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We have 3 offences for PushRule controllers relating to namespace nesting.

https://gitlab.com/gitlab-org/gitlab/-/blob/399901149d67a2f33c623c55e07c273c2f152cfe/.rubocop_todo/style/class_and_module_children.yml#L356

https://gitlab.com/gitlab-org/gitlab/-/blob/399901149d67a2f33c623c55e07c273c2f152cfe/.rubocop_todo/style/class_and_module_children.yml#L390

https://gitlab.com/gitlab-org/gitlab/-/blob/399901149d67a2f33c623c55e07c273c2f152cfe/.rubocop_todo/style/class_and_module_children.yml#L414