test_default_policy_is_tablet_aware: Reorder a few operations

I want to introduce retries in case of schema migrations. It will be
easier if per-attempt operations are together, separate from one-time
setup.

Author: Lorak-mmk

scylla/tests/integration/load_balancing/tablets.rs

@@ -293,15 +293,11 @@ async fn test_default_policy_is_tablet_aware() {
             /* Prepare schema */
             prepare_schema(&session, &ks, "t", TABLET_COUNT).await;
 
-            let tablets = get_tablets(&session, &ks, "t").await;
-
             let prepared = session
                 .prepare(format!("INSERT INTO {ks}.t (a, b, c) VALUES (?, ?, 'abc')"))
                 .await
                 .unwrap();
 
-            let value_lists = calculate_key_per_tablet(&tablets, &prepared);
-
             let (feedback_txs, mut feedback_rxs): (Vec<_>, Vec<_>) = (0..3)
                 .map(|_| mpsc::unbounded_channel::<(ResponseFrame, Option<TargetShard>)>())
                 .unzip();
@@ -313,6 +309,9 @@ async fn test_default_policy_is_tablet_aware() {
                 )]));
             }
 
+            let tablets = get_tablets(&session, &ks, "t").await;
+            let value_lists = calculate_key_per_tablet(&tablets, &prepared);
+
             populate_internal_driver_tablet_info(
                 &session,
                 &prepared,