Review Request: CALCITE-5064

[Charles Givre]

Hello Calcite Devs, 
I'd like to request a review for CALCITE-5064 
(https://github.com/apache/calcite/pull/2752 
<https://github.com/apache/calcite/pull/2752>) which is a minor bug fix that 
prevents the correct dialect from being selected for BigQuery. 
Thanks!
-- C