Update unit test due to change in name of the upstream exec function

Author: timsaucer

python/tests/test_dataframe.py

@@ -752,7 +752,7 @@ def test_execution_plan(aggregate_df):
     assert "AggregateExec:" in indent
     assert "CoalesceBatchesExec:" in indent
     assert "RepartitionExec:" in indent
-    assert "CsvExec:" in indent
+    assert "DataSourceExec:" in indent
 
     ctx = SessionContext()
     rows_returned = 0