fix test mypy

Author: fresioAS

tests/core/test_context.py

@@ -334,7 +334,7 @@ def test_render_only_loads_upstream_model_files(tmp_path: pathlib.Path) -> None:
     Context(config=config, paths=tmp_path, load=False).load(use_project_index=True)
 
     ctx = Context(config=config, paths=tmp_path, load=False)
-    loader = ctx._loaders[0]
+    loader = t.cast(SqlMeshLoader, ctx._loaders[0])
     with patch.object(
         loader,
         "_load_sql_models",