Bleeding edge Tailscale Nix flake broke after updating to go1.20rc3.
Go 1.20 moved to Go 1.17 as a bootstarp toolchain. Fortunately nixpkgs
nixos-unstable already had a 1.20.nix with bootstrap117.nix.
```
❯ ./result/bin/tailscale version
1.37.0-dev
track: unstable (dev); frequent updates and bugs are likely
go version: go1.20rc3-ts6a17f14c05
```
Signed-off-by: Shayne Sweeney <shayne@tailscale.com>
With this, you can import "github:tailscale/tailscale" as a nix flake,
and get access to the "tailscale-unstable" package.
Updates #6845.
Signed-off-by: David Anderson <dave@natulte.net>
