Update dependency google-cloud-pubsub to v1.4.2 [(#3336)](GoogleCloudPlatform/python-docs-samples#3336)

Co-authored-by: Leah E. Cole <6719667+leahecole@users.noreply.github.com>

Author: busunkim96

packages/google-cloud-asset/samples/snippets/requirements.txt

@@ -1,4 +1,4 @@
 google-cloud-storage==1.26.0
 google-cloud-asset==0.9.0
 google-cloud-resource-manager==0.30.1
-google-cloud-pubsub==1.1.0
+google-cloud-pubsub==1.4.2