Update nbformat/validator.py

Co-authored-by: Paul Ivanov <[email protected]>

nbformat/validator.py

@@ -342,7 +342,7 @@ def iter_validate(nbdict=None, ref=None, version=None, version_minor=None,
                             error_for_intended_schema = error.schema_path[0] == schema_index
                             is_top_level_metadata_key = len(rel_path) == 2 and rel_path[0] == "metadata"
                             if error_for_intended_schema and is_top_level_metadata_key:
-                                nbdict["cells"][cell_idx][rel_path[0]].pop(rel_path[1], None)
+                                nbdict["cells"][cell_idx]["metadata"].pop(rel_path[1], None)
 
             # Validate one more time to ensure that us removing metadata
             # didn't cause another complex validation issue in the schema.