Fix assertion in test_show_from_empty_batch to ensure proper output for empty DataFrames

Author: kosiew

python/tests/test_dataframe.py

@@ -2678,4 +2678,4 @@ def test_show_from_empty_batch(capsys) -> None:
     batch = pa.record_batch([pa.array([], type=pa.int32())], names=["a"])
     ctx.create_dataframe([[batch]]).show()
     out = capsys.readouterr().out
-    assert "| a |" in out
+    assert "| a |" in out