OCIS_ADMIN_USER_ID is not updated when a role is already present

[micbar]

Describe the bug

A clear and concise description of what the bug is.

Steps to reproduce

1. Set up oCIS with an external IdP with autorprivisioning and PROXY_ROLE_ASSIGNMENT_DRIVER=default
2. Login with the first user from the IdP
3. Lookup the user UUID for this user and set it via OCIS_ADMIN_USER_ID=<desired-admin-user-id>

Expected behavior

The desigated admin should have the admin role assigned

Actual behavior

When there is a role assigned already, which happens during autoprovisioning, the admin role is not enforced by updating it.

[micbar]

Fix in #8897