chore(deps): update dependency pytest to v5.4.3 [(#4279)](GoogleCloudPlatform/python-docs-samples#4279)

* chore(deps): update dependency pytest to v5.4.3

* specify pytest for python 2 in appengine

Co-authored-by: Leah Cole <[email protected]>

Author: renovate-bot

samples/snippets/v3/alerts-client/requirements-test.txt

@@ -1,3 +1,3 @@
-pytest==5.3.2
+pytest==5.4.3
 retrying==1.3.3
 flaky==3.6.1

samples/snippets/v3/api-client/requirements-test.txt

@@ -1,3 +1,3 @@
 backoff==1.10.0
-pytest==5.3.2
+pytest==5.4.3
 flaky==3.6.1

samples/snippets/v3/cloud-client/requirements-test.txt

@@ -1,3 +1,3 @@
 backoff==1.10.0
-pytest==5.3.2
+pytest==5.4.3
 mock==3.0.5