chore: fix pytest crash on pandas 3.0 due to missing SettingWithCopyWarning

The `SettingWithCopyWarning` has been removed in pandas 3.0. Having it in `pytest.ini`'s `filterwarnings` caused pytest to crash on startup when resolving the warning class. This change moves the suppression to `conftest.py` where it is applied conditionally only if the warning class exists.

Author: google-labs-jules[bot]

conftest.py

@@ -14,13 +14,20 @@
 
 from __future__ import annotations
 
+import warnings
+
 import numpy as np
 import pandas as pd
 import pyarrow as pa
 import pytest
 
 import bigframes._config
 
+# Make sure SettingWithCopyWarning is ignored if it exists.
+# It was removed in pandas 3.0.
+if hasattr(pd.errors, "SettingWithCopyWarning"):
+    warnings.simplefilter("ignore", pd.errors.SettingWithCopyWarning)
+
 
 @pytest.fixture(scope="session")
 def polars_session_or_bpd():

pytest.ini

@@ -1,5 +1,3 @@
 [pytest]
 doctest_optionflags = NORMALIZE_WHITESPACE
-filterwarnings =
-    ignore::pandas.errors.SettingWithCopyWarning
 addopts = "--import-mode=importlib"