tests: replace mock with unittest.mock

ckanext/dc_serve/tests/test_jobs.py

@@ -7,7 +7,7 @@
 ckan.plugins.toolkit.enqueue_job function with a mock that executes jobs
 synchronously instead of asynchronously
 """
-import mock
+from unittest import mock
 import pathlib
 
 import pytest

ckanext/dc_serve/tests/test_route.py

@@ -1,4 +1,4 @@
-import mock
+from unittest import mock
 
 import ckan.common
 import ckan.model

ckanext/dc_serve/tests/test_serve.py

@@ -1,6 +1,6 @@
 import copy
 import json
-import mock
+from unittest import mock
 import shutil
 import uuid