backend adaptations due to cox change role

src/model/tripdetails.rs

@@ -146,7 +146,7 @@ WHERE day = ? AND planned_starting_time = ?
                     // User is a guest, no need to bother.
                     continue;
                 };
-                if !user.has_role(db, "cox").await {
+                if !user.allowed_to_steer(db).await {
                     // User is no cox, no need to bother
                     continue;
                 }