Bump moto version to try solve dependencies version conflict

Also update mock import statements in some test files as they
stopped working with this dependency update.

tests/app/celery/test_scheduled_tasks.py

@@ -1,10 +1,10 @@
 from collections import namedtuple
 from datetime import datetime, timedelta
+from unittest import mock
 from unittest.mock import call
 
 import pytest
 from freezegun import freeze_time
-from mock import mock
 
 from app.celery import scheduled_tasks
 from app.celery.scheduled_tasks import (