chore(lint): remove unused imports flagged by ruff

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/core/test_git_askpass.py

@@ -1,5 +1,4 @@
 """Unit tests for GIT_ASKPASS injection in git_pull()."""
-import asyncio
 import os
 import stat
 from pathlib import Path

tests/core/test_inventory_gen.py

@@ -3,7 +3,6 @@
 Uses SimpleNamespace duck-typed objects so no DB or SQLAlchemy is required.
 """
 from types import SimpleNamespace
-import pytest
 from steward.ansible.inventory_gen import generate_inventory