More fixes

Author: shanejbrown

buildrunner/docker/multiplatform_image_builder.py

@@ -77,7 +77,7 @@ def __init__(
         docker_registry: Optional[str] = None,
         build_registry: Optional[str] = MP_LOCAL_REGISTRY,
         temp_dir: str = os.getcwd(),
-        platform_builders: Optional[Union[Dict[str, List[str]], List[str]]] = None,
+        platform_builders: Optional[Union[Dict[str, List[str]], Dict[str, str]]] = None,
         cache_builders: Optional[List[str]] = None,
         cache_from: Optional[Union[dict, str]] = None,
         cache_to: Optional[Union[dict, str]] = None,