Fix mypy type errors in regression test

Co-Authored-By: [email protected] <[email protected]>

Author: devin-ai-integration[bot]

ee/vellum_ee/workflows/display/tests/workflow_serialization/test_partial_workflow_meta_display_override.py

@@ -43,7 +43,9 @@ class TestWorkflowDisplay(BaseWorkflowDisplay[TestWorkflow]):
     entrypoint_node = entrypoint_nodes[0]
     assert isinstance(entrypoint_node, dict)
     assert entrypoint_node["id"] is not None, "ENTRYPOINT node should have a non-None id"
-    source_handle_id = entrypoint_node["data"]["source_handle_id"]
+    entrypoint_data = entrypoint_node["data"]
+    assert isinstance(entrypoint_data, dict)
+    source_handle_id = entrypoint_data["source_handle_id"]
     assert source_handle_id is not None, "ENTRYPOINT node should have a non-None source_handle_id"
 
     # AND there should be an edge from ENTRYPOINT to the process node