Fix mypy unreachable-statement error in PuffinWriter exception test

Restructure test_puffin_writer_does_not_write_on_exception to use
try/except instead of nesting an unconditional raise inside
pytest.raises, which mypy's warn-unreachable flagged as unreachable.

Co-authored-by: Isaac

Author: moomindani

tests/table/test_puffin.py

@@ -144,13 +144,15 @@ def test_puffin_writer_empty(tmp_path: Path) -> None:
 
 
 def test_puffin_writer_does_not_write_on_exception(tmp_path: Path) -> None:
-    puffin_path = tmp_path / "test.puffin"
-    output_file = PyArrowFileIO().new_output(str(puffin_path))
+    output_file = PyArrowFileIO().new_output(str(tmp_path / "test.puffin"))
+    writer = PuffinWriter(output_file)
 
-    with pytest.raises(ValueError, match="boom"):
-        with PuffinWriter(output_file) as writer:
+    try:
+        with writer:
             writer.add_blob(DeletionVector.from_positions("file.parquet", [1]).to_blob())
             raise ValueError("boom")
+    except ValueError:
+        pass
 
     assert writer.closed
     # The body raised, so no half-populated file should have been written.