[Rails5] Fix spec/models/project_services/kubernetes_service_spec.rb

Note: add rails5 to a branch name to trigger rails5 specific CI jobs.

https://gitlab.com/gitlab-org/gitlab-ce/-/jobs/67501616

  2) KubernetesService Validations with an active and deprecated service should update attributes
     Failure/Error: expect(kubernetes_service.properties[:namespace]).to eq("foo")

       expected: "foo"
            got: nil

       (compared using ==)
     # ./spec/models/project_services/kubernetes_service_spec.rb:108:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:144:in `block (2 levels) in <top (required)>'

  3) KubernetesService Validations with a template service should update attributes
     Failure/Error: expect(kubernetes_service.properties[:namespace]).to eq('foo')

       expected: "foo"
            got: nil

       (compared using ==)
     # ./spec/models/project_services/kubernetes_service_spec.rb:121:in `block (4 levels) in <top (required)>'
     # ./spec/spec_helper.rb:144:in `block (2 levels) in <top (required)>'