Add test coverage to `app/assets/javascripts/work_items/graphql/resolvers.js`

The following discussion from !160153 (merged) should be addressed:

• @leetickett-gitlab started a discussion:

  @deepika.guliani @ntepluhina would y'all mind doing the review/maintainerizing please? 🙏

  There's no directly test suite for this file- should we create one or is it testing via other test suites?