cmd/racebuild: use 9.0 netbsd builders

They have the increased disk space this script needs to work.

Change-Id: I782fc121db0326c5dc1c267d08fd7320f38c65b6
Reviewed-on: https://go-review.googlesource.com/c/build/+/227546
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/cmd/racebuild/racebuild.go b/cmd/racebuild/racebuild.go
index 73ec9f2..e60a5a3 100644
--- a/cmd/racebuild/racebuild.go
+++ b/cmd/racebuild/racebuild.go
@@ -135,7 +135,7 @@
 	&Platform{
 		OS:   "netbsd",
 		Arch: "amd64",
-		Type: "netbsd-amd64-8_0",
+		Type: "netbsd-amd64-9_0",
 		Script: `#!/usr/bin/env bash
 set -e
 git clone https://go.googlesource.com/go