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 <bk@golangcn.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Meng Zhuo <mzh@golangcn.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Trust: Bryan C. Mills <bcmills@google.com>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 5a0cffa..714cb8e 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -659,7 +659,7 @@
 		Notes:       "Windows 10 WSL2 Ubuntu",
 		OwnerGithub: "mengzhuo",
 		IsReverse:   true,
-		ExpectNum:   1,
+		ExpectNum:   2,
 		env:         []string{"GOROOT_BOOTSTRAP=/usr/lib/go"},
 	},
 }