chore(deps): update dependency google-cloud-pubsub to v2.15.2 (#1009)

Author: renovate-bot

samples/snippets/requirements.txt

@@ -1,4 +1,4 @@
-google-cloud-pubsub==2.15.1
+google-cloud-pubsub==2.15.2
 google-cloud-storage==2.7.0
 pandas===1.3.5; python_version == '3.7'
 pandas==1.5.3; python_version >= '3.8'