chore(deps): update dependency google-cloud-bigquery to v2.20.0 (#317)

Author: renovate-bot

samples/snippets/requirements.txt

@@ -1,4 +1,4 @@
 google-cloud-logging==2.4.0
-google-cloud-bigquery==2.18.0
+google-cloud-bigquery==2.20.0
 google-cloud-storage==1.38.0
 google-cloud-pubsub==2.5.0