chore: cleanup catching non-existent return value (#2202)

[kk-src]

Please describe the purpose of this pull request.

Fixes issue #2202. The user_manager.list_users returns the combined user list, without next cursor. This patch cleans up the code to not capture non-existent return value and thus fixes the listing of users.

How to test

Listing users will succeed.

Have you tested this PR?

Tested by running the server locally and using curl to get the users. Here is the relevant snippet:

curl -X GET -L "http://127.0.0.1:8283/v1/admin/users"
[{"id":"user-00000000-0000-4000-8000-000000000000","organization_id":"org-00000000-0000-4000-8000-000000000000","name":"default_user",......

Related issues or PRs

#2202

Is your PR over 500 lines of code?
N/A

Additional context
A future TODO (if needed) is to add tests for list users. At the moment due to 7ad5f01 the test are broken (gives ModuleNotFoundError: No module named 'openai').