fix: remove unused imports (flake8 F401) and replace hardcoded test password

Agent-Logs-Url: https://github.com/christianlouis/dmarq/sessions/72367edf-35f7-4c7c-a5ff-bbe4909b2139

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/app/tests/test_security_extra.py

@@ -6,14 +6,12 @@ create_access_token, and require_admin_auth branches not yet exercised.
 from datetime import timedelta
 
 import pytest
-from fastapi.testclient import TestClient
 from jose import jwt
 
 from app.core.security import (
     add_api_key,
     create_access_token,
     generate_api_key,
-    verify_api_key,
     verify_token,
 )