Fix typing of field upgrade_messages in one of the return models of t…

…he workflow_dict operation

lib/galaxy/schema/workflows.py

@@ -833,7 +833,7 @@ class WorkflowDictPreviewSummary(WorkflowDictExtendedBaseModel):
 
 
 class WorkflowDictEditorSummary(WorkflowDictExtendedBaseModel):
-    upgrade_messages: Dict[int, str] = Field(
+    upgrade_messages: Dict[int, Union[str, Dict[str, str]]] = Field(
         ...,
         title="Upgrade Messages",
         description="Upgrade messages for each step in the workflow.",