Fix obvious typo in test wheel generator

Author: sbidoul

tests/lib/wheel.py

@@ -102,7 +102,7 @@ def make_metadata_file(
     if body is not _default:
         message.set_payload(body)
 
-    return File(path, message_from_dict(metadata).as_bytes())
+    return File(path, message.as_bytes())
 
 
 def make_wheel_metadata_file(