Fix flaky work item policy spec

What does this MR do and why?

This MR fixes a flaky work item policy spec discovered with scripts/rspec_check_order_dependence via RSPEC_ORDER=reverse bin/rspec ./spec/policies/work_item_policy_spec.rb. See the bisect'ed version below.

How to set up and validate locally

bin/rspec ./spec/policies/work_item_policy_spec.rb[1:3:2:1,1:5:2:3:1] --seed 17644

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.