[TODO] Spell out the selected package index upload URL in error output visibly

[webknjaz]

I wonder if we can have a sanity check for this… Your job run has repository_url: https://upload.pypi.org/legacy/ in the log, which is our default. And GitHub Actions is built to choose defaults if an empty string is passed. I don't think we can detect this programmatically, but maybe printing out a big warning “You're attempting to upload to ” on errors would make improve the experience…

cc @woodruffw

Originally posted by @webknjaz in #336 (reply in thread)