remove exception-returning since it overwrites fail_on_error

src/transformers/wiki_dump_handler.py

@@ -98,5 +98,4 @@ class WikiDumpHandler(xml.sax.ContentHandler):
         # Write to all handlers concurrently
         await asyncio.gather(
             *[handler.write_entry(entry, uid) for handler in self.handlers],
-            return_exceptions = True,
         )