chore: fix docs build

Author: tswast

.coveragerc

@@ -14,7 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Generated by synthtool. DO NOT EDIT!
 [run]
 branch = True
 omit =
@@ -34,6 +33,5 @@ exclude_lines =
 omit =
   */gapic/*.py
   */proto/*.py
-  */core/*.py
   */site-packages/*.py
   google/cloud/__init__.py

pandas_gbq/gbq.py

@@ -419,9 +419,7 @@ def to_gbq(
     destination_table : str
         Name of table to be written, in the form ``dataset.tablename`` or
         ``project.dataset.tablename``.
-    clustering_columns: typing.Union[
-        pandas.core.indexes.base.Index, typing.Iterable[typing.Hashable]
-    ] = (),
+    clustering_columns: pandas.Index | Iterable[Hashable]
         Specifies the columns for clustering in the BigQuery table.
     time_partitioning_column : str, optional
         Specifies the column for time-based partitioning in the BigQuery table.

tests/unit/core/__init__.py

@@ -0,0 +1,3 @@
+# Copyright (c) 2026 pandas-gbq Authors All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.