During the release of xmonad 0.17.0, I realized that we need to be able
to upload candidates before tagging the release on GitHub, because there
might be issues with the tarball and Hackage may reject it. When that
happened, I had to remove the release, delete the tag, upload the
candidate manually to see what's wrong with it, try to fix it, upload it
manually again, and so on.
This commit swaps the logic: when the workflow is invoked manually, it
uploads the candidate. This can be done multiple times, and once
everything is fine, the release can finally be tagged and it's released
to Hackage proper. The only disadvantage is that we need to remember to
try uploading the candidate. Not sure if there's a perfect solution…
