[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Author: pre-commit-ci[bot]

cl/tests/base.py

@@ -20,7 +20,6 @@
 from timeout_decorator import TimeoutError
 
 from cl.lib.decorators import retry
-from cl.lib.test_helpers import SerializeLockFileTestMixin
 from cl.search.models import SEARCH_TYPES
 from cl.tests.cases import ESIndexTestCase, StaticLiveServerTestCase