oauth2: add test-sandbox.auth.corp.google.com to the broken providers

Change-Id: I1d2e1ea803283b5651a482445b9be60262b43c4e
Reviewed-on: https://go-review.googlesource.com/9343
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/internal/token.go b/internal/token.go
index 2ed6bd3..727d957 100644
--- a/internal/token.go
+++ b/internal/token.go
@@ -107,6 +107,7 @@
 	"https://oauth.trainingpeaks.com/",
 	"https://www.strava.com/oauth/",
 	"https://app.box.com/",
+	"https://test-sandbox.auth.corp.google.com",
 }
 
 // providerAuthHeaderWorks reports whether the OAuth2 server identified by the tokenURL