chore(deps): update dependency google-cloud-pubsub to v2.3.0 (#176)

Author: renovate-bot

samples/snippets/requirements.txt

@@ -1,4 +1,4 @@
 google-cloud-logging==2.2.0
 google-cloud-storage==1.35.1
-google-cloud-pubsub==2.2.0
+google-cloud-pubsub==2.3.0
 google-cloud-bigquery==2.7.0