fix mypy typing using lepture/mistune#375

schema_salad/makedoc.py

@@ -18,6 +18,7 @@
     Set,
     Tuple,
     Union,
+    cast,
 )
 from urllib.parse import urldefrag
 
@@ -606,7 +607,7 @@ def extendsfrom(item: Dict[str, Any], ex: List[Dict[str, Any]]) -> None:
             escape=escape,
         )
         ##markdown2html.before_parse_hooks.append(markdown_list_hook)  # FIXME: this can be removed with mistune v3!
-        doc = markdown2html(doc)
+        doc = cast(str, markdown2html(doc))
 
         if f["type"] == "record":
             doc += "<h3>Fields</h3>"