Tag nightlies as prerelease releases (#3892)
This does 2 main things:
- Sets each nightly release as a prerelease on GH's [releases](https://github.com/vercel/turbo/releases) page
- Adds a [notice annotation](https://www.npmjs.com/package/@actions/core#:~:text=These%20will%20surface%20to%20the%20UI%20in%20the%20Actions%20page%20and%20on%20Pull%20Requests.%20They%20look%20something%20like%20this%3A) to the workflow, so that the new tag is logged in the workflow's execution
Additionally, it fixes the `pnpm` workspace so that the action's dist code is actually built. This also means we'll finally see the output of https://github.com/vercel/turbo/pull/3819 in our release bodies.
