tests: cleanup test code

- remove unused imports in test cases
- fix code smells and code style in conftest.py

test/test_debug_endpoint/test_global.py

@@ -1,6 +1,8 @@
 import json
+
 import pytest
 
+
 def test_debug_endpoint_is_enabled_globally(docker_compose, nginxproxy):
     r = nginxproxy.get("http://enabled.debug.nginx-proxy.example/nginx-proxy-debug")
     assert r.status_code == 200

test/test_debug_endpoint/test_per_container.py

@@ -1,6 +1,8 @@
 import json
+
 import pytest
 
+
 def test_debug_endpoint_is_disabled_globally(docker_compose, nginxproxy):
     r = nginxproxy.get("http://disabled1.debug.nginx-proxy.example/nginx-proxy-debug")
     assert r.status_code == 404