fix(doc): suppress BigQuery logs in sim_join doctest

Author: shuoweil

bigframes/operations/ai.py

@@ -612,11 +612,11 @@ def sim_join(
             >>> df1 = bpd.DataFrame({'animal': ['monkey', 'spider']})
             >>> df2 = bpd.DataFrame({'animal': ['scorpion', 'baboon']})
 
-            >>> print("START_OF_OUTPUT"); df1.ai.sim_join(df2, left_on='animal', right_on='animal', model=model, top_k=1) # doctest: +ELLIPSIS,+NORMALIZE_WHITESPACE
-            START_OF_OUTPUT
+            >>> res = df1.ai.sim_join(df2, left_on='animal', right_on='animal', model=model, top_k=1)
+            >>> print("---"); print(res) # doctest: +ELLIPSIS
+            ---
             ...
                animal  animal_1
-            ...
             0  monkey    baboon
             1  spider  scorpion
             <BLANKLINE>