Hardcoding to `prerelease: true` is a holdover from before we had
migrated to the Rust CLI for releases and decided on how we were doing
version numbers.
To date, I have had to change the release status from "prerelease" to
"actual release" manually through the GitHub Releases web page. This is
a semi-serious problem because I've discovered that it messes up
Homebrew's automation if the version number _looks_ like a real release
but turns out to be a prerelease. The release potentially gets skipped
from being published on Homebrew, so it's important to set the value
correctly from the start.
I verified that `steps.release_name.outputs.name` does not include the
`rust-v` prefix from the tag name.
493e4c9463