[fix](regression) Sync version 3 before DROP in test_clean_tablet_when_drop_force_table (#69846)

Related PR: #68449

Problem Summary:

`test_clean_tablet_when_drop_force_table` fails intermittently with
`File cache directories were not cleaned before timeout`. The leftover
cache dirs all belong to the version 3 rowsets.

#68449 set `disable_auto_compaction=true` for this case. Before that
change, cloud compaction called `sync_rowsets()` and loaded version 3
into the BE tablets as a side effect. Now nothing loads version 3
between the second stream load and `DROP TABLE FORCE`, because the case
only queries after the version 2 load. The cloud `drop_tablet_callback`
only recycles the file cache of rowsets in `get_snapshot_rowset(true)`,
so the version 3 cache stays and the cleanup assertion times out.

This PR queries the table after the version 3 load, the same way the
case already does after version 2. The query loads version 3 on every BE
before DROP. It also asserts the row count (160000) to confirm version 3
is visible.

regression-test/suites/cloud_p0/tablets/test_clean_tablet_when_drop_force_table.groovy

@@ -282,6 +282,16 @@ suite('test_clean_tablet_when_drop_force_table', 'docker') {
             }
         }
 
+        // Auto compaction is disabled, so nothing else syncs version 3 into the BE tablets.
+        // DROP only recycles the file cache of rowsets already loaded on the BE, so query
+        // here to load version 3 before collecting its cache dirs.
+        for (int i = 0; i < 5; i++) {
+            def rows = sql """
+                select count(*) from $tableName
+            """
+            assertEquals(160000L, rows[0][0] as long)
+        }
+
         // before drop table force
         def beforeGetFromFe = getTabletAndBeHostFromFe(tableName)
         def beforeGetFromBe = getTabletAndBeHostFromBe(cluster.getAllBackends())