User sessions: local user session shows as "Generic OAuth" in Auth Provider column

### What happened? When querying a user's sessions using the admin API or when viewing a user's sessions from the Users and Access area, local (i.e. internal Grafana) users will show "Generic OAuth" in the Auth Provider column, even if they are not using any external authentication. This seems to only happen when other users are logged in with a Generic OAuth provider. If no other users are not logged in, the local user shows nothing under the Identity Provider heading as expected. ### What did you expect to happen? Local users should not show any external identity provider for their sessions. ### Did this work before? I don't think so. ### How do we reproduce it? 1. Log in to Grafana with a local user. 2. In a separate browser session, log into Grafana with a Generic OAuth user. 3. View the local user's session information under Administration > Users and Access > Users > Sessions. It will show the "Generic OAuth" label for each session, despite this authentication mechanism not being used by this particular user. ### Is the bug inside a dashboard panel? No. ### Environment (with versions)? Grafana: 12.0.2+security-01 OS: Ubuntu 24.04 Browser: Firefox 142.0.1 ### Grafana platform? A package manager (APT, YUM, BREW, etc.) ### Datasource(s)? Not specific to a datasource.