Update src/replit_river/codegen/client.py

Co-authored-by: Devon Stewart <devon.stewart@repl.it>

Author: airportyh

src/replit_river/codegen/client.py

@@ -768,9 +768,9 @@ def append_type_adapter_definition(
         type_adapter_name: TypeName,
         _type: TypeExpression,
         module_info: list[ModuleName],
-    ) -> None:
+    ) -> tuple[list[TypeName], list[ModuleName], list[FileContents]]:
         rendered_type_expr = render_type_expr(_type)
-        serdes.append(
+        return (
             (
                 [type_adapter_name],
                 module_info,