API: Return 404 if user does not have access to group
Closes #15185
After !3587 (merged) is merged, I'll update this one to also fix the return code of the tests in !3587 (merged).
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Closes #15185
After !3587 (merged) is merged, I'll update this one to also fix the return code of the tests in !3587 (merged).