chore(deps): update dependency google-cloud-pubsub to v1.4.3 [(#3725)](…

…GoogleCloudPlatform/python-docs-samples#3725)

Co-authored-by: Bu Sun Kim <8822365+busunkim96@users.noreply.github.com>
Co-authored-by: Takashi Matsuo <tmatsuo@google.com>

samples/snippets/requirements.txt

@@ -1,5 +1,5 @@
 google-cloud-dlp==0.14.0
 google-cloud-storage==1.28.0
-google-cloud-pubsub==1.4.2
+google-cloud-pubsub==1.4.3
 google-cloud-datastore==1.12.0
 google-cloud-bigquery==1.24.0