tests: alphabetize and group Python imports & add check

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

tests/http/testenv/env.py

@@ -33,14 +33,13 @@ import subprocess
 import tempfile
 from configparser import ConfigParser, ExtendedInterpolation
 from datetime import timedelta
-from typing import Optional, Dict, List
+from typing import Dict, List, Optional
 
 import pytest
 from filelock import FileLock
 
 from .certs import CertificateSpec, Credentials, TestCA
 
-
 log = logging.getLogger(__name__)