fixes mypy

Author: pcrespov

packages/models-library/src/models_library/projects_nodes.py

@@ -478,6 +478,7 @@ def _update_json_schema_extra(schema: JsonDict) -> None:
 
 
 class PartialNode(Node):
-    key: ServiceKey | None = None
-    version: ServiceVersion | None = None
-    label: str | None = None
+    # NOTE: `type: ignore[assignment]` is needed because mypy gets confused when overriding the types by adding the Union with None
+    key: ServiceKey | None = None  # type: ignore[assignment]
+    version: ServiceVersion | None = None  # type: ignore[assignment]
+    label: str | None = None  # type: ignore[assignment]