chore: skip orc test if pyarrow.orc is not available

The pyarrow.orc module is an optional extension that isn't available internally.

Author: tswast

tests/unit/test_dataframe_polars.py

@@ -4193,6 +4193,7 @@ def test_df_to_pickle(scalars_df_index, scalars_pandas_df_index):
 
 
 def test_df_to_orc(scalars_df_index, scalars_pandas_df_index):
+    pytest.importorskip("pyarrow.orc")
     unsupported = [
         "numeric_col",
         "bytes_col",