Artifact download URL when using --deploy=local is wrong

[aviks]

When running build_tarballs.jl with a --deploy=local option, the resulting Artifact.toml has the artifact download url set to something like this: https://github.com/local/releases/download/MyPkg-v0.2.1+1/MyPkg.v0.2.1.aarch64-apple-darwin.tar.gz

Now the right value here is unkown so it's not clear what should happen. Maybe some more affordances to let the user know that this value should be changed? https://github.com/CHANGE/ME/releases/downloads.... . The current value is plausible enough to be dangerous, IMO.