new typescript actions creates artifacts in repo

The new typescript action creates artifacts in the local repo, the tailscale.tgz and tailscaled.pid files. In most cases, that's probably not a big deal, but for actions that are updating files in the local repo and then opening PRs, those files get included in the PR. For example, our internal http://go/golink-snapshot action. For now, I've added those to our .gitignore file, which is fine, but it might be nice to store those elsewhere if possible?

If you want to be really pedantic about it, tailscale.tgz should probably be put in XDG_CACHE_HOME (default: ~/.cache) and tailscaled.pid should be in XDG_RUNTIME_DIR, which I don't think has a canonical default. On my system, it's set to /run/user/1000, but that might be an arch thing. We might need to experiment with what gets set on action runners, or just simply putting it in ~/.cache too would likely be fine.

Start by tracing the TypeScript action's creation of tailscale.tgz and tailscaled.pid, then inspect the repository .gitignore and the action runner's available XDG directories. Determine a suitable location outside the local repository for both artifacts, and verify that an action updating files can open a PR without including them.