replace google cloud mysql entry with a more accurate one

Author: markingmyname

articles/migration/index.yml

@@ -201,6 +201,9 @@ conceptualContent:
           - url: /azure/postgresql/migrate/migration-service/tutorial-migration-service-cloud-sql-online
             text: Migrate Cloud SQL for PostgreSQL to Azure Database for PostgreSQL (online)
             itemType: tutorial
+          - url: /azure/dms/tutorial-mysql-azure-mysql-offline-portal
+            text: Migrate Cloud SQL for MySQL to Azure Database for MySQL (offline)
+            itemType: tutorial
         footerLink:
           text: See more
           url: ./migrate-databases-from-google-cloud.md