[Bug] "Legacy Storage" error when migrating dashboards from 11.1.0 to 12.3.0

What happened? After upgrading from Grafana OSS 11.1.0 to 12.3.0, I am encountering a "Legacy Storage" error when accessing specific dashboards or attempting to save changes. This seems to block the migration of dashboard metadata or alert rules attached to them. What was expected? Dashboards should migrate seamlessly to the new schema without throwing storage legacy errors. Steps to reproduce: Upgrade Grafana from 11.1.0 to 12.3.0. Open a dashboard that was created in the previous version. Attempt to save or view alert rules. Error "Legacy Storage" appears. Environment: Grafana version: 12.3.0 OSS OS: [Tu Sistema Operativo, ej. Linux/Docker]