Replace loop test fixture with event_loop
This addresses a deprecation warning when calling tests with Python
3.10:
```
../python3.10/site-packages/pytest_aiohttp/plugin.py:33: DeprecationWarning: 'loop' fixture is deprecated and scheduled for removal, please use 'event_loop' instead
```
@@ -225,7 +225,9 @@ async def resolved(dbus: DBus) -> Resolved:
@pytest.fixture
-async def coresys(loop, docker, network_manager, aiohttp_client, run_dir) -> CoreSys:
+async def coresys(
+ event_loop, docker, network_manager, aiohttp_client, run_dir
+) -> CoreSys:
"""Create a CoreSys Mock."""
with patch("supervisor.bootstrap.initialize_system"), patch(
"supervisor.bootstrap.setup_diagnostics"
