chore(deps): update dependency google-cloud-bigquery to v2.15.0 (#277)

Author: renovate-bot

samples/snippets/requirements.txt

@@ -1,4 +1,4 @@
 google-cloud-logging==2.3.1
-google-cloud-bigquery==2.14.0
+google-cloud-bigquery==2.15.0
 google-cloud-storage==1.37.1
 google-cloud-pubsub==2.4.1