chore(deps): update dependency google-cloud-pubsub to v2.12.0 (#758)

Author: renovate-bot

samples/snippets/requirements.txt

@@ -1,4 +1,4 @@
-google-cloud-pubsub==2.11.0
+google-cloud-pubsub==2.12.0
 google-cloud-storage==2.2.1
 pandas===1.3.5; python_version == '3.7'
 pandas==1.4.2; python_version >= '3.8'