This tweaks the just-added ./tool/go.{cmd,ps1} port of ./tool/go for
Windows.
Otherwise in Windows Terminal in Powershell, running just ".\tool\go"
picks up go.ps1 before go.cmd, which means execution gets denied
without the cmd script's -ExecutionPolicy Bypass part letting it work.
This makes it work in both cmd.exe and in Powershell.
Updates tailscale/corp#28679
Change-Id: Iaf628a9fd6cb95670633b2dbdb635dfb8afaa006
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
