convert.py: warning goes to stderr and won't hurt the dump output

Author: mofosyne

convert.py

@@ -1476,7 +1476,7 @@ def main(args_in: list[str] | None = None) -> None:
         logging.basicConfig(level=logging.DEBUG)
     elif args.dump_single or args.dump:
         # Avoid printing anything besides the dump output
-        logging.basicConfig(level=logging.CRITICAL)
+        logging.basicConfig(level=logging.WARNING)
     else:
         logging.basicConfig(level=logging.INFO)