Stabilize import order for packaging.

I don't want to consider it a dependency of transformers, but it's
usually there in local development and usually not there in CI.

setup.cfg

@@ -3,6 +3,7 @@ ensure_newline_before_comments = True
 force_grid_wrap = 0
 include_trailing_comma = True
 known_first_party = transformers
+known_third_party = packaging
 line_length = 119
 lines_after_imports = 2
 multi_line_output = 3