chore: set a maximum number of rows for BigQuery query results in the sample agent

The `BigQueryToolConfig` now sets `max_query_result_rows=50` explicitly to showcase this particular configuration.

PiperOrigin-RevId: 871709345

Author: google-genai-bot

contributing/samples/bigquery/agent.py

@@ -38,7 +38,9 @@
 # tool read-only) or PROTECTED (only allows writes in the anonymous dataset of a
 # BigQuery session) write mode.
 tool_config = BigQueryToolConfig(
-    write_mode=WriteMode.ALLOWED, application_name=BIGQUERY_AGENT_NAME
+    write_mode=WriteMode.ALLOWED,
+    application_name=BIGQUERY_AGENT_NAME,
+    max_query_result_rows=50,
 )
 
 if CREDENTIALS_TYPE == AuthCredentialTypes.OAUTH2: