tool: rename go.ps1 to go-win.ps1 for cmd.exe+Powershell compat

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>

tool/go.cmd

@@ -1,2 +1,2 @@
 @echo off
-powershell -NoProfile -ExecutionPolicy Bypass -File "%~dp0go.ps1" %*
+powershell -NoProfile -ExecutionPolicy Bypass -File "%~dp0go-win.ps1" %*