Improve brittle admin user API test

[svenaas]

Improve the Admin Users API with the hope of preventing an inconsistent failure.

Notes

The Admin Users API test is inconsistently and infrequently failing in Concourse with

  1) Admin - Users API
       GET /admin/reports/active-users.csv
         returns all users with UAA identities:
     AssertionError: expected [ …(2) ] to include '70,"[email protected]","org-16|org-17…'
      at Context.<anonymous> (test/api/admin/requests/user.test.js:204:23)
      at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

I have not been able to reproduce locally, but hope to prevent this failure through improvement to the test.

Acceptance Criteria

• [x] Test improved
• [ ] We experience a decent interval without this test failing unexpectedly