dashboard: add a new wsl builder to improve service availability

For golang/go#17365

Change-Id: Icf776550e3f17d86bf0f74d5598912fe1a18cb50
Reviewed-on: https://go-review.googlesource.com/c/build/+/278874
Run-TryBot: Baokun Lee <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Bryan C. Mills <[email protected]>
Reviewed-by: Meng Zhuo <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>
Trust: Bryan C. Mills <[email protected]>

Author: oiooj

dashboard/builders.go

@@ -659,7 +659,7 @@ var Hosts = map[string]*HostConfig{
 		Notes:       "Windows 10 WSL2 Ubuntu",
 		OwnerGithub: "mengzhuo",
 		IsReverse:   true,
-		ExpectNum:   1,
+		ExpectNum:   2,
 		env:         []string{"GOROOT_BOOTSTRAP=/usr/lib/go"},
 	},
 }