fix a bug where we return incorrectly

Signed-off-by: Trishank K Kuppusamy <trishank.kuppusamy@datadoghq.com>

tuf/client/updater.py

@@ -1132,14 +1132,14 @@ def _update_root_metadata(self, current_root_metadata):
     """
 
     def neither_403_nor_404(mirror_error):
+      WHITELIST = {403, 404}
       if isinstance(mirror_error, six.moves.urllib.error.HTTPError):
-        if mirror_error.code in {403, 404}:
+        if mirror_error.code in WHITELIST:
           return False
       elif isinstance(mirror_error, requests.exceptions.HTTPError):
-        if mirror_error.response.status_code in {403, 404}:
+        if mirror_error.response.status_code in WHITELIST:
           return False
-      else:
-        return True
+      return True
 
     # Temporarily set consistent snapshot. Will be updated to whatever is set
     # in the latest root.json after running through the intermediates with