app/appengine, dashboard: add x/website subrepo

Updates golang/go#30640

Change-Id: I2926f45efa18530ce72fa4a7ecdc255839bd6f45
Reviewed-on: https://go-review.googlesource.com/c/build/+/177658
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/dashboard/builders_test.go b/dashboard/builders_test.go
index 57c0a45..e3425e2 100644
--- a/dashboard/builders_test.go
+++ b/dashboard/builders_test.go
@@ -266,6 +266,7 @@
 		{b("linux-amd64", "go"), both},
 		{b("linux-amd64", "net"), both},
 		{b("linux-amd64", "sys"), both},
+		{b("linux-amd64", "website"), both},
 
 		// Don't test all subrepos on all the builders.
 		{b("linux-amd64-ssacheck", "net"), none},