[tools][cts] Limit requested scopes for cache bucket

We only need read-write access. Should fix issues where non-admins get permission errors.

Change-Id: I6148b6c66628ad7dff1211ef049c6d21dc42c745
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/158242
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/tools/src/cmd/cts/common/cache.go b/tools/src/cmd/cts/common/cache.go
index dec6608..7efc78e 100644
--- a/tools/src/cmd/cts/common/cache.go
+++ b/tools/src/cmd/cts/common/cache.go
@@ -67,7 +67,8 @@
 		return "", err
 	}
 
-	client, err := storage.NewClient(ctx, option.WithTokenSource(ts))
+	client, err := storage.NewClient(ctx, option.WithTokenSource(ts),
+		option.WithScopes(storage.ScopeReadWrite))
 	if err != nil {
 		return "", fmt.Errorf("failed to create google cloud storage client: %w", err)
 	}