chore(deps): update dependency google-cloud-pubsub to v1.4.3 [(#3725)](GoogleCloudPlatform/python-docs-samples#3725)

Co-authored-by: Bu Sun Kim <[email protected]>
Co-authored-by: Takashi Matsuo <[email protected]>

Author: 3 people

samples/snippets/requirements.txt

@@ -1 +1 @@
-google-cloud-pubsub==1.4.2
+google-cloud-pubsub==1.4.3