test: don't rely on output batch count in test_sort_with_streaming_table

SortPreservingMergeStream now forwards the last remaining stream's
batches as-is, so the number of output batches is not guaranteed.
Concatenate the result batches before comparing values.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: rluvaton

datafusion/core/tests/physical_optimizer/enforce_sorting.rs

@@ -2839,10 +2839,11 @@ async fn test_sort_with_streaming_table() -> Result<()> {
     let sql = "SELECT a FROM test_table GROUP BY a ORDER BY a";
     let results = ctx.sql(sql).await?.collect().await?;
 
-    assert_eq!(results.len(), 1);
-    assert_eq!(results[0].num_columns(), 1);
+    // The number of output batches is not guaranteed, so concatenate before comparing
+    let results = arrow::compute::concat_batches(&results[0].schema(), &results)?;
+    assert_eq!(results.num_columns(), 1);
     let expected = create_array!(Int32, vec![1, 2, 3]) as ArrayRef;
-    assert_eq!(results[0].column(0), &expected);
+    assert_eq!(results.column(0), &expected);
 
     Ok(())
 }