chore: some lint fixes [(#3748)](GoogleCloudPlatform/python-docs-samples#3748)

Author: Takashi Matsuo

samples/snippets/v3/api-client/custom_metric_test.py

@@ -27,8 +27,8 @@
 
 import backoff
 import googleapiclient.discovery
-import pytest
 from googleapiclient.errors import HttpError
+import pytest
 
 from custom_metric import create_custom_metric
 from custom_metric import delete_metric_descriptor

samples/snippets/v3/cloud-client/snippets_test.py

@@ -14,10 +14,10 @@
 
 import os
 import re
-import pytest
 
 import backoff
 from google.api_core.exceptions import NotFound
+import pytest
 
 import snippets