Rename struct in read_only_field_visibility test

Author: Nilirad

crates/bevy_ecs/src/query/fetch.rs

@@ -1601,14 +1601,14 @@ mod tests {
 
             #[derive(WorldQueryData)]
             #[world_query_data(mutable)]
-            pub struct Q {
+            pub struct D {
                 pub a: &'static mut A,
             }
         }
 
         let _ = private::QReadOnly { a: &A };
 
-        fn my_system(query: Query<private::Q>) {
+        fn my_system(query: Query<private::D>) {
             for q in &query {
                 let _ = &q.a;
             }