tests: alphabetize and group Python imports & add check

- De-duplicates, groups, and sorts imports based on the provided `isort` settings.

tests/http/test_05_errors.py

@@ -26,10 +26,9 @@
 #
 import logging
 import os
+
 import pytest
-
-from testenv import Env, CurlClient
-
+from testenv import CurlClient, Env
 
 log = logging.getLogger(__name__)