PAM sometimes exits with exit code 4 after successful authentication (in tests)

[adombeck]

Examples:

• https://github.com/ubuntu/authd/actions/runs/17411484775/job/49429491900?pr=1046#step:14:4619

== Authentication code ==
Enter 'r' to cancel the request and go back to select the authentication method
Enter your one time credential:
> temporary pass00
PAM Authenticate()
  User: "user-integration-native-authenticate-user-with-form-mode-with-button-in-polkit"
  Result: success
PAM AcctMgmt()
  User: "user-integration-native-authenticate-user-with-form-mode-with-button-in-polkit"
  Result: error: PAM exit code: 4
    System error
>