Fix tests failing due to underfined ordering

[zetter-rpf]

This test is failing in [1] because the student ids were in a different order.

Make sure the test accepts ids in any order.

[1] - https://app.circleci.com/pipelines/github/RaspberryPiFoundation/editor-api/2948/workflows/88d009c2-3b67-46a9-8dc5-cc248bfe5df0/jobs/5600?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-checks-link&utm_content=summary

Logs

  1) SchoolStudent::List without student_ids makes a profile API call
     Failure/Error: expect(ProfileApiClient).to have_received(:list_school_students).with(token:, school_id: school.id, student_ids: students.map(&:id))
     
       #<ProfileApiClient (class)> received :list_school_students with unexpected arguments
         expected: ({:school_id=>"ebdee3e8-ecf9-4927-bd44-d7d7727b2cd4", :student_ids=>["a686fc94-c7f6-437f-bcd3-c30449c3...-4129-b858-144d2312a8b0", "13d649ab-33d1-48a8-bbad-08fcfc090ab5"], :token=>"fake-user-access-token"}) (options hash)
              got: ({:school_id=>"ebdee3e8-ecf9-4927-bd44-d7d7727b2cd4", :student_ids=>["13d649ab-33d1-48a8-bbad-08fcfc09...-4129-b858-144d2312a8b0", "a686fc94-c7f6-437f-bcd3-c30449c3e241"], :token=>"fake-user-access-token"}) (keyword arguments)
       Diff:
       
       @@ -1,6 +1,6 @@
        [{:school_id=>"ebdee3e8-ecf9-4927-bd44-d7d7727b2cd4",
          :student_ids=>
       -   ["a686fc94-c7f6-437f-bcd3-c30449c3e241",
       +   ["13d649ab-33d1-48a8-bbad-08fcfc090ab5",
            "351b87b4-a3a4-4129-b858-144d2312a8b0",
       -    "13d649ab-33d1-48a8-bbad-08fcfc090ab5"],
       +    "a686fc94-c7f6-437f-bcd3-c30449c3e241"],
          :token=>"fake-user-access-token"}]
       
     # ./spec/concepts/school_student/list_spec.rb:27:in `block (3 levels) in <top (required)>'