use cached property instead of custom __getattr__ implementation

tests/ahriman/application/handlers/test_handler_validate.py

@@ -61,11 +61,14 @@ def test_schema(configuration: Configuration) -> None:
     assert schema.pop("console")
     assert schema.pop("email")
     assert schema.pop("github")
+    assert schema.pop("gitremote")
     assert schema.pop("html")
     assert schema.pop("keyring")
     assert schema.pop("keyring_generator")
     assert schema.pop("mirrorlist")
     assert schema.pop("mirrorlist_generator")
+    assert schema.pop("remote-pull")
+    assert schema.pop("remote-push")
     assert schema.pop("report")
     assert schema.pop("rsync")
     assert schema.pop("s3")