Fix TestIcebergInsert.testIcebergConcurrentInsert timeout on CI

The test seems dominated by `finishInsert` time. since
bf04a72 `finishInsert` is slower as we
commit twice (first committing data then statistics).

testing/trino-product-tests/src/main/java/io/trino/tests/product/iceberg/TestIcebergInsert.java

@@ -50,7 +50,7 @@ public void testIcebergConcurrentInsert()
             throws Exception
     {
         int threads = 3;
-        int insertsPerThread = 7;
+        int insertsPerThread = 4;
 
         String tableName = "iceberg.default.test_insert_concurrent_" + randomNameSuffix();
         onTrino().executeQuery("CREATE TABLE " + tableName + "(a bigint)");